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• How to Write a Strong Hypothesis | Steps & Examples

How to Write a Strong Hypothesis | Steps & Examples

Published on May 6, 2022 by Shona McCombes . Revised on November 20, 2023.

A hypothesis is a statement that can be tested by scientific research. If you want to test a relationship between two or more variables, you need to write hypotheses before you start your experiment or data collection .

Example: Hypothesis

Daily apple consumption leads to fewer doctor’s visits.

Table of contents

What is a hypothesis, developing a hypothesis (with example), hypothesis examples, other interesting articles, frequently asked questions about writing hypotheses.

A hypothesis states your predictions about what your research will find. It is a tentative answer to your research question that has not yet been tested. For some research projects, you might have to write several hypotheses that address different aspects of your research question.

A hypothesis is not just a guess – it should be based on existing theories and knowledge. It also has to be testable, which means you can support or refute it through scientific research methods (such as experiments, observations and statistical analysis of data).

Variables in hypotheses

Hypotheses propose a relationship between two or more types of variables .

• An independent variable is something the researcher changes or controls.
• A dependent variable is something the researcher observes and measures.

If there are any control variables , extraneous variables , or confounding variables , be sure to jot those down as you go to minimize the chances that research bias  will affect your results.

In this example, the independent variable is exposure to the sun – the assumed cause . The dependent variable is the level of happiness – the assumed effect .

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Step 1. ask a question.

Writing a hypothesis begins with a research question that you want to answer. The question should be focused, specific, and researchable within the constraints of your project.

Step 2. Do some preliminary research

Your initial answer to the question should be based on what is already known about the topic. Look for theories and previous studies to help you form educated assumptions about what your research will find.

At this stage, you might construct a conceptual framework to ensure that you’re embarking on a relevant topic . This can also help you identify which variables you will study and what you think the relationships are between them. Sometimes, you’ll have to operationalize more complex constructs.

Step 3. Formulate your hypothesis

Now you should have some idea of what you expect to find. Write your initial answer to the question in a clear, concise sentence.

4. Refine your hypothesis

You need to make sure your hypothesis is specific and testable. There are various ways of phrasing a hypothesis, but all the terms you use should have clear definitions, and the hypothesis should contain:

• The relevant variables
• The specific group being studied
• The predicted outcome of the experiment or analysis

5. Phrase your hypothesis in three ways

To identify the variables, you can write a simple prediction in  if…then form. The first part of the sentence states the independent variable and the second part states the dependent variable.

In academic research, hypotheses are more commonly phrased in terms of correlations or effects, where you directly state the predicted relationship between variables.

If you are comparing two groups, the hypothesis can state what difference you expect to find between them.

6. Write a null hypothesis

If your research involves statistical hypothesis testing , you will also have to write a null hypothesis . The null hypothesis is the default position that there is no association between the variables. The null hypothesis is written as H 0 , while the alternative hypothesis is H 1 or H a .

• H 0 : The number of lectures attended by first-year students has no effect on their final exam scores.
• H 1 : The number of lectures attended by first-year students has a positive effect on their final exam scores.

If you want to know more about the research process , methodology , research bias , or statistics , make sure to check out some of our other articles with explanations and examples.

• Sampling methods
• Simple random sampling
• Stratified sampling
• Cluster sampling
• Likert scales
• Reproducibility

 Statistics

• Null hypothesis
• Statistical power
• Probability distribution
• Effect size
• Poisson distribution

Research bias

• Optimism bias
• Cognitive bias
• Implicit bias
• Hawthorne effect
• Anchoring bias
• Explicit bias

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A hypothesis is not just a guess — it should be based on existing theories and knowledge. It also has to be testable, which means you can support or refute it through scientific research methods (such as experiments, observations and statistical analysis of data).

Null and alternative hypotheses are used in statistical hypothesis testing . The null hypothesis of a test always predicts no effect or no relationship between variables, while the alternative hypothesis states your research prediction of an effect or relationship.

Hypothesis testing is a formal procedure for investigating our ideas about the world using statistics. It is used by scientists to test specific predictions, called hypotheses , by calculating how likely it is that a pattern or relationship between variables could have arisen by chance.

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Scientific Hypothesis Examples

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A hypothesis is an educated guess about what you think will happen in a scientific experiment, based on your observations. Before conducting the experiment, you propose a hypothesis so that you can determine if your prediction is supported.

There are several ways you can state a hypothesis, but the best hypotheses are ones you can test and easily refute. Why would you want to disprove or discard your own hypothesis? Well, it is the easiest way to demonstrate that two factors are related. Here are some good scientific hypothesis examples:

• Hypothesis: All forks have three tines. This would be disproven if you find any fork with a different number of tines.
• Hypothesis: There is no relationship between smoking and lung cancer. While it is difficult to establish cause and effect in health issues, you can apply statistics to data to discredit or support this hypothesis.
• Hypothesis: Plants require liquid water to survive. This would be disproven if you find a plant that doesn't need it.
• Hypothesis: Cats do not show a paw preference (equivalent to being right- or left-handed). You could gather data around the number of times cats bat at a toy with either paw and analyze the data to determine whether cats, on the whole, favor one paw over the other. Be careful here, because individual cats, like people, might (or might not) express a preference. A large sample size would be helpful.
• Hypothesis: If plants are watered with a 10% detergent solution, their growth will be negatively affected. Some people prefer to state a hypothesis in an "If, then" format. An alternate hypothesis might be: Plant growth will be unaffected by water with a 10% detergent solution.
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Hypothesis Examples

A hypothesis is a prediction of the outcome of a test. It forms the basis for designing an experiment in the scientific method . A good hypothesis is testable, meaning it makes a prediction you can check with observation or experimentation. Here are different hypothesis examples.

Null Hypothesis Examples

The null hypothesis (H 0 ) is also known as the zero-difference or no-difference hypothesis. It predicts that changing one variable ( independent variable ) will have no effect on the variable being measured ( dependent variable ). Here are null hypothesis examples:

• Plant growth is unaffected by temperature.
• If you increase temperature, then solubility of salt will increase.
• Incidence of skin cancer is unrelated to ultraviolet light exposure.
• All brands of light bulb last equally long.
• Cats have no preference for the color of cat food.
• All daisies have the same number of petals.

Sometimes the null hypothesis shows there is a suspected correlation between two variables. For example, if you think plant growth is affected by temperature, you state the null hypothesis: “Plant growth is not affected by temperature.” Why do you do this, rather than say “If you change temperature, plant growth will be affected”? The answer is because it’s easier applying a statistical test that shows, with a high level of confidence, a null hypothesis is correct or incorrect.

Research Hypothesis Examples

A research hypothesis (H 1 ) is a type of hypothesis used to design an experiment. This type of hypothesis is often written as an if-then statement because it’s easy identifying the independent and dependent variables and seeing how one affects the other. If-then statements explore cause and effect. In other cases, the hypothesis shows a correlation between two variables. Here are some research hypothesis examples:

• If you leave the lights on, then it takes longer for people to fall asleep.
• If you refrigerate apples, they last longer before going bad.
• If you keep the curtains closed, then you need less electricity to heat or cool the house (the electric bill is lower).
• If you leave a bucket of water uncovered, then it evaporates more quickly.
• Goldfish lose their color if they are not exposed to light.
• Workers who take vacations are more productive than those who never take time off.

Is It Okay to Disprove a Hypothesis?

Yes! You may even choose to write your hypothesis in such a way that it can be disproved because it’s easier to prove a statement is wrong than to prove it is right. In other cases, if your prediction is incorrect, that doesn’t mean the science is bad. Revising a hypothesis is common. It demonstrates you learned something you did not know before you conducted the experiment.

Test yourself with a Scientific Method Quiz .

• Mellenbergh, G.J. (2008). Chapter 8: Research designs: Testing of research hypotheses. In H.J. Adèr & G.J. Mellenbergh (eds.), Advising on Research Methods: A Consultant’s Companion . Huizen, The Netherlands: Johannes van Kessel Publishing.
• Popper, Karl R. (1959). The Logic of Scientific Discovery . Hutchinson & Co. ISBN 3-1614-8410-X.
• Schick, Theodore; Vaughn, Lewis (2002). How to think about weird things: critical thinking for a New Age . Boston: McGraw-Hill Higher Education. ISBN 0-7674-2048-9.
• Tobi, Hilde; Kampen, Jarl K. (2018). “Research design: the methodology for interdisciplinary research framework”. Quality & Quantity . 52 (3): 1209–1225. doi: 10.1007/s11135-017-0513-8

Related Posts

How to Develop a Good Research Hypothesis

The story of a research study begins by asking a question. Researchers all around the globe are asking curious questions and formulating research hypothesis. However, whether the research study provides an effective conclusion depends on how well one develops a good research hypothesis. Research hypothesis examples could help researchers get an idea as to how to write a good research hypothesis.

This blog will help you understand what is a research hypothesis, its characteristics and, how to formulate a research hypothesis

Table of Contents

What is Hypothesis?

Hypothesis is an assumption or an idea proposed for the sake of argument so that it can be tested. It is a precise, testable statement of what the researchers predict will be outcome of the study.  Hypothesis usually involves proposing a relationship between two variables: the independent variable (what the researchers change) and the dependent variable (what the research measures).

What is a Research Hypothesis?

Research hypothesis is a statement that introduces a research question and proposes an expected result. It is an integral part of the scientific method that forms the basis of scientific experiments. Therefore, you need to be careful and thorough when building your research hypothesis. A minor flaw in the construction of your hypothesis could have an adverse effect on your experiment. In research, there is a convention that the hypothesis is written in two forms, the null hypothesis, and the alternative hypothesis (called the experimental hypothesis when the method of investigation is an experiment).

Characteristics of a Good Research Hypothesis

As the hypothesis is specific, there is a testable prediction about what you expect to happen in a study. You may consider drawing hypothesis from previously published research based on the theory.

A good research hypothesis involves more effort than just a guess. In particular, your hypothesis may begin with a question that could be further explored through background research.

To help you formulate a promising research hypothesis, you should ask yourself the following questions:

• Is the language clear and focused?
• What is the relationship between your hypothesis and your research topic?
• Is your hypothesis testable? If yes, then how?
• What are the possible explanations that you might want to explore?
• Does your hypothesis include both an independent and dependent variable?
• Can you manipulate your variables without hampering the ethical standards?
• Does your research predict the relationship and outcome?
• Is your research simple and concise (avoids wordiness)?
• Is it clear with no ambiguity or assumptions about the readers’ knowledge
• Is your research observable and testable results?
• Is it relevant and specific to the research question or problem?

The questions listed above can be used as a checklist to make sure your hypothesis is based on a solid foundation. Furthermore, it can help you identify weaknesses in your hypothesis and revise it if necessary.

Source: Educational Hub

How to formulate a research hypothesis.

A testable hypothesis is not a simple statement. It is rather an intricate statement that needs to offer a clear introduction to a scientific experiment, its intentions, and the possible outcomes. However, there are some important things to consider when building a compelling hypothesis.

1. State the problem that you are trying to solve.

Make sure that the hypothesis clearly defines the topic and the focus of the experiment.

2. Try to write the hypothesis as an if-then statement.

Follow this template: If a specific action is taken, then a certain outcome is expected.

3. Define the variables

Independent variables are the ones that are manipulated, controlled, or changed. Independent variables are isolated from other factors of the study.

Dependent variables , as the name suggests are dependent on other factors of the study. They are influenced by the change in independent variable.

4. Scrutinize the hypothesis

Evaluate assumptions, predictions, and evidence rigorously to refine your understanding.

Types of Research Hypothesis

The types of research hypothesis are stated below:

1. Simple Hypothesis

It predicts the relationship between a single dependent variable and a single independent variable.

2. Complex Hypothesis

It predicts the relationship between two or more independent and dependent variables.

3. Directional Hypothesis

It specifies the expected direction to be followed to determine the relationship between variables and is derived from theory. Furthermore, it implies the researcher’s intellectual commitment to a particular outcome.

4. Non-directional Hypothesis

It does not predict the exact direction or nature of the relationship between the two variables. The non-directional hypothesis is used when there is no theory involved or when findings contradict previous research.

5. Associative and Causal Hypothesis

The associative hypothesis defines interdependency between variables. A change in one variable results in the change of the other variable. On the other hand, the causal hypothesis proposes an effect on the dependent due to manipulation of the independent variable.

6. Null Hypothesis

Null hypothesis states a negative statement to support the researcher’s findings that there is no relationship between two variables. There will be no changes in the dependent variable due the manipulation of the independent variable. Furthermore, it states results are due to chance and are not significant in terms of supporting the idea being investigated.

7. Alternative Hypothesis

It states that there is a relationship between the two variables of the study and that the results are significant to the research topic. An experimental hypothesis predicts what changes will take place in the dependent variable when the independent variable is manipulated. Also, it states that the results are not due to chance and that they are significant in terms of supporting the theory being investigated.

Research Hypothesis Examples of Independent and Dependent Variables

Research Hypothesis Example 1 The greater number of coal plants in a region (independent variable) increases water pollution (dependent variable). If you change the independent variable (building more coal factories), it will change the dependent variable (amount of water pollution).

Research Hypothesis Example 2 What is the effect of diet or regular soda (independent variable) on blood sugar levels (dependent variable)? If you change the independent variable (the type of soda you consume), it will change the dependent variable (blood sugar levels)

You should not ignore the importance of the above steps. The validity of your experiment and its results rely on a robust testable hypothesis. Developing a strong testable hypothesis has few advantages, it compels us to think intensely and specifically about the outcomes of a study. Consequently, it enables us to understand the implication of the question and the different variables involved in the study. Furthermore, it helps us to make precise predictions based on prior research. Hence, forming a hypothesis would be of great value to the research. Here are some good examples of testable hypotheses.

More importantly, you need to build a robust testable research hypothesis for your scientific experiments. A testable hypothesis is a hypothesis that can be proved or disproved as a result of experimentation.

Importance of a Testable Hypothesis

To devise and perform an experiment using scientific method, you need to make sure that your hypothesis is testable. To be considered testable, some essential criteria must be met:

• There must be a possibility to prove that the hypothesis is true.
• There must be a possibility to prove that the hypothesis is false.
• The results of the hypothesis must be reproducible.

Without these criteria, the hypothesis and the results will be vague. As a result, the experiment will not prove or disprove anything significant.

What are your experiences with building hypotheses for scientific experiments? What challenges did you face? How did you overcome these challenges? Please share your thoughts with us in the comments section.

Frequently Asked Questions

The steps to write a research hypothesis are: 1. Stating the problem: Ensure that the hypothesis defines the research problem 2. Writing a hypothesis as an 'if-then' statement: Include the action and the expected outcome of your study by following a ‘if-then’ structure. 3. Defining the variables: Define the variables as Dependent or Independent based on their dependency to other factors. 4. Scrutinizing the hypothesis: Identify the type of your hypothesis

Hypothesis testing is a statistical tool which is used to make inferences about a population data to draw conclusions for a particular hypothesis.

Hypothesis in statistics is a formal statement about the nature of a population within a structured framework of a statistical model. It is used to test an existing hypothesis by studying a population.

Research hypothesis is a statement that introduces a research question and proposes an expected result. It forms the basis of scientific experiments.

The different types of hypothesis in research are: • Null hypothesis: Null hypothesis is a negative statement to support the researcher’s findings that there is no relationship between two variables. • Alternate hypothesis: Alternate hypothesis predicts the relationship between the two variables of the study. • Directional hypothesis: Directional hypothesis specifies the expected direction to be followed to determine the relationship between variables. • Non-directional hypothesis: Non-directional hypothesis does not predict the exact direction or nature of the relationship between the two variables. • Simple hypothesis: Simple hypothesis predicts the relationship between a single dependent variable and a single independent variable. • Complex hypothesis: Complex hypothesis predicts the relationship between two or more independent and dependent variables. • Associative and casual hypothesis: Associative and casual hypothesis predicts the relationship between two or more independent and dependent variables. • Empirical hypothesis: Empirical hypothesis can be tested via experiments and observation. • Statistical hypothesis: A statistical hypothesis utilizes statistical models to draw conclusions about broader populations.

Wow! You really simplified your explanation that even dummies would find it easy to comprehend. Thank you so much.

Thanks a lot for your valuable guidance.

I enjoy reading the post. Hypotheses are actually an intrinsic part in a study. It bridges the research question and the methodology of the study.

Useful piece!

This is awesome.Wow.

It very interesting to read the topic, can you guide me any specific example of hypothesis process establish throw the Demand and supply of the specific product in market

Nicely explained

It is really a useful for me Kindly give some examples of hypothesis

It was a well explained content ,can you please give me an example with the null and alternative hypothesis illustrated

clear and concise. thanks.

So Good so Amazing

Good to learn

Thanks a lot for explaining to my level of understanding

Explained well and in simple terms. Quick read! Thank you

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5.2 - writing hypotheses.

The first step in conducting a hypothesis test is to write the hypothesis statements that are going to be tested. For each test you will have a null hypothesis (\(H_0\)) and an alternative hypothesis (\(H_a\)).

When writing hypotheses there are three things that we need to know: (1) the parameter that we are testing (2) the direction of the test (non-directional, right-tailed or left-tailed), and (3) the value of the hypothesized parameter.

• At this point we can write hypotheses for a single mean (\(\mu\)), paired means(\(\mu_d\)), a single proportion (\(p\)), the difference between two independent means (\(\mu_1-\mu_2\)), the difference between two proportions (\(p_1-p_2\)), a simple linear regression slope (\(\beta\)), and a correlation (\(\rho\)). 
• The research question will give us the information necessary to determine if the test is two-tailed (e.g., "different from," "not equal to"), right-tailed (e.g., "greater than," "more than"), or left-tailed (e.g., "less than," "fewer than").
• The research question will also give us the hypothesized parameter value. This is the number that goes in the hypothesis statements (i.e., \(\mu_0\) and \(p_0\)). For the difference between two groups, regression, and correlation, this value is typically 0.

Hypotheses are always written in terms of population parameters (e.g., \(p\) and \(\mu\)).  The tables below display all of the possible hypotheses for the parameters that we have learned thus far. Note that the null hypothesis always includes the equality (i.e., =).

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What do you want to find out about your study site’s water quality, how will I measure it and what are your predictions?

Check Your Thinking: Scenario: There is an abandoned mine dump within 5 meters of your study site stream. How might contaminants in the mine waste be impacting your stream? When would be the best time of year/day to collect water monitoring data that could help answer this question? What tests should you conduct?

Using your recorded observations and information compiled in the first step, the next step is to come up with a testable question. You can use the previously mentioned question (Based on what I know about the pH, DO, temperature and turbidity of my site, is the water of a good enough quality to support aquatic life?) as it relates to the limitations of the World Water Monitoring Day kit, or come up with one of your own.

What results do you predict? For example, your hypothesis may be “I believe the pH, DO, temperature and turbidity of the water at my study site are of good enough quality to support aquatic life because there are no visible impacts to water quality upstream or on the site.” Once you’ve formulated your question, begin planning the experiment or, in this case, the water monitoring you will conduct .

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How to Write a Great Hypothesis

Hypothesis Format, Examples, and Tips

Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Amy Morin, LCSW, is a psychotherapist and international bestselling author. Her books, including "13 Things Mentally Strong People Don't Do," have been translated into more than 40 languages. Her TEDx talk,  "The Secret of Becoming Mentally Strong," is one of the most viewed talks of all time.

Verywell / Alex Dos Diaz

• The Scientific Method

Hypothesis Format

Falsifiability of a hypothesis, operational definitions, types of hypotheses, hypotheses examples.

• Collecting Data

Frequently Asked Questions

A hypothesis is a tentative statement about the relationship between two or more  variables. It is a specific, testable prediction about what you expect to happen in a study.

One hypothesis example would be a study designed to look at the relationship between sleep deprivation and test performance might have a hypothesis that states: "This study is designed to assess the hypothesis that sleep-deprived people will perform worse on a test than individuals who are not sleep-deprived."

This article explores how a hypothesis is used in psychology research, how to write a good hypothesis, and the different types of hypotheses you might use.

The Hypothesis in the Scientific Method

In the scientific method , whether it involves research in psychology, biology, or some other area, a hypothesis represents what the researchers think will happen in an experiment. The scientific method involves the following steps:

• Forming a question
• Performing background research
• Creating a hypothesis
• Designing an experiment
• Collecting data
• Analyzing the results
• Drawing conclusions
• Communicating the results

The hypothesis is a prediction, but it involves more than a guess. Most of the time, the hypothesis begins with a question which is then explored through background research. It is only at this point that researchers begin to develop a testable hypothesis. Unless you are creating an exploratory study, your hypothesis should always explain what you  expect  to happen.

In a study exploring the effects of a particular drug, the hypothesis might be that researchers expect the drug to have some type of effect on the symptoms of a specific illness. In psychology, the hypothesis might focus on how a certain aspect of the environment might influence a particular behavior.

Remember, a hypothesis does not have to be correct. While the hypothesis predicts what the researchers expect to see, the goal of the research is to determine whether this guess is right or wrong. When conducting an experiment, researchers might explore a number of factors to determine which ones might contribute to the ultimate outcome.

In many cases, researchers may find that the results of an experiment  do not  support the original hypothesis. When writing up these results, the researchers might suggest other options that should be explored in future studies.

In many cases, researchers might draw a hypothesis from a specific theory or build on previous research. For example, prior research has shown that stress can impact the immune system. So a researcher might hypothesize: "People with high-stress levels will be more likely to contract a common cold after being exposed to the virus than people who have low-stress levels."

In other instances, researchers might look at commonly held beliefs or folk wisdom. "Birds of a feather flock together" is one example of folk wisdom that a psychologist might try to investigate. The researcher might pose a specific hypothesis that "People tend to select romantic partners who are similar to them in interests and educational level."

Elements of a Good Hypothesis

So how do you write a good hypothesis? When trying to come up with a hypothesis for your research or experiments, ask yourself the following questions:

• Is your hypothesis based on your research on a topic?
• Can your hypothesis be tested?
• Does your hypothesis include independent and dependent variables?

Before you come up with a specific hypothesis, spend some time doing background research. Once you have completed a literature review, start thinking about potential questions you still have. Pay attention to the discussion section in the  journal articles you read . Many authors will suggest questions that still need to be explored.

To form a hypothesis, you should take these steps:

• Collect as many observations about a topic or problem as you can.
• Evaluate these observations and look for possible causes of the problem.
• Create a list of possible explanations that you might want to explore.
• After you have developed some possible hypotheses, think of ways that you could confirm or disprove each hypothesis through experimentation. This is known as falsifiability.

In the scientific method ,  falsifiability is an important part of any valid hypothesis.   In order to test a claim scientifically, it must be possible that the claim could be proven false.

Students sometimes confuse the idea of falsifiability with the idea that it means that something is false, which is not the case. What falsifiability means is that  if  something was false, then it is possible to demonstrate that it is false.

One of the hallmarks of pseudoscience is that it makes claims that cannot be refuted or proven false.

A variable is a factor or element that can be changed and manipulated in ways that are observable and measurable. However, the researcher must also define how the variable will be manipulated and measured in the study.

For example, a researcher might operationally define the variable " test anxiety " as the results of a self-report measure of anxiety experienced during an exam. A "study habits" variable might be defined by the amount of studying that actually occurs as measured by time.

These precise descriptions are important because many things can be measured in a number of different ways. One of the basic principles of any type of scientific research is that the results must be replicable.   By clearly detailing the specifics of how the variables were measured and manipulated, other researchers can better understand the results and repeat the study if needed.

Some variables are more difficult than others to define. How would you operationally define a variable such as aggression ? For obvious ethical reasons, researchers cannot create a situation in which a person behaves aggressively toward others.

In order to measure this variable, the researcher must devise a measurement that assesses aggressive behavior without harming other people. In this situation, the researcher might utilize a simulated task to measure aggressiveness.

Hypothesis Checklist

• Does your hypothesis focus on something that you can actually test?
• Does your hypothesis include both an independent and dependent variable?
• Can you manipulate the variables?
• Can your hypothesis be tested without violating ethical standards?

The hypothesis you use will depend on what you are investigating and hoping to find. Some of the main types of hypotheses that you might use include:

• Simple hypothesis : This type of hypothesis suggests that there is a relationship between one independent variable and one dependent variable.
• Complex hypothesis : This type of hypothesis suggests a relationship between three or more variables, such as two independent variables and a dependent variable.
• Null hypothesis : This hypothesis suggests no relationship exists between two or more variables.
• Alternative hypothesis : This hypothesis states the opposite of the null hypothesis.
• Statistical hypothesis : This hypothesis uses statistical analysis to evaluate a representative sample of the population and then generalizes the findings to the larger group.
• Logical hypothesis : This hypothesis assumes a relationship between variables without collecting data or evidence.

A hypothesis often follows a basic format of "If {this happens} then {this will happen}." One way to structure your hypothesis is to describe what will happen to the  dependent variable  if you change the  independent variable .

The basic format might be: "If {these changes are made to a certain independent variable}, then we will observe {a change in a specific dependent variable}."

A few examples of simple hypotheses:

• "Students who eat breakfast will perform better on a math exam than students who do not eat breakfast."
• Complex hypothesis: "Students who experience test anxiety before an English exam will get lower scores than students who do not experience test anxiety."​
• "Motorists who talk on the phone while driving will be more likely to make errors on a driving course than those who do not talk on the phone."

Examples of a complex hypothesis include:

• "People with high-sugar diets and sedentary activity levels are more likely to develop depression."
• "Younger people who are regularly exposed to green, outdoor areas have better subjective well-being than older adults who have limited exposure to green spaces."

Examples of a null hypothesis include:

• "Children who receive a new reading intervention will have scores different than students who do not receive the intervention."
• "There will be no difference in scores on a memory recall task between children and adults."

Examples of an alternative hypothesis:

• "Children who receive a new reading intervention will perform better than students who did not receive the intervention."
• "Adults will perform better on a memory task than children." 

Collecting Data on Your Hypothesis

Once a researcher has formed a testable hypothesis, the next step is to select a research design and start collecting data. The research method depends largely on exactly what they are studying. There are two basic types of research methods: descriptive research and experimental research.

Descriptive Research Methods

Descriptive research such as  case studies ,  naturalistic observations , and surveys are often used when it would be impossible or difficult to  conduct an experiment . These methods are best used to describe different aspects of a behavior or psychological phenomenon.

Once a researcher has collected data using descriptive methods, a correlational study can then be used to look at how the variables are related. This type of research method might be used to investigate a hypothesis that is difficult to test experimentally.

Experimental Research Methods

Experimental methods  are used to demonstrate causal relationships between variables. In an experiment, the researcher systematically manipulates a variable of interest (known as the independent variable) and measures the effect on another variable (known as the dependent variable).

Unlike correlational studies, which can only be used to determine if there is a relationship between two variables, experimental methods can be used to determine the actual nature of the relationship—whether changes in one variable actually  cause  another to change.

A Word From Verywell

The hypothesis is a critical part of any scientific exploration. It represents what researchers expect to find in a study or experiment. In situations where the hypothesis is unsupported by the research, the research still has value. Such research helps us better understand how different aspects of the natural world relate to one another. It also helps us develop new hypotheses that can then be tested in the future.

Some examples of how to write a hypothesis include:

• "Staying up late will lead to worse test performance the next day."
• "People who consume one apple each day will visit the doctor fewer times each year."
• "Breaking study sessions up into three 20-minute sessions will lead to better test results than a single 60-minute study session."

The four parts of a hypothesis are:

• The research question
• The independent variable (IV)
• The dependent variable (DV)
• The proposed relationship between the IV and DV

Castillo M. The scientific method: a need for something better? . AJNR Am J Neuroradiol. 2013;34(9):1669-71. doi:10.3174/ajnr.A3401

Nevid J. Psychology: Concepts and Applications. Wadworth, 2013.

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

May 24, 2018

Mix It Up with Oil and Water

A science shake-up activity from Science Buddies

By Science Buddies & Megan Arnett

A little mixup: Use kitchen chemistry to make oil and water blend. 

George Retseck

Key concepts Chemistry Surfactants Density Polarity

Introduction You may have heard people say, “Those two mix like oil and water,” when they’re describing two people who don’t get along. Maybe you’ve also noticed shiny oil floating on the surface of water puddles after it rains. In both cases you understand that water and oil don’t go well together—but have you ever wondered why? So many other things can dissolve in water—why not oil? In this activity we’ll explore what makes oil so special, and we’ll try making the impossible happen: mixing oil and water!

Background Unlike many other substances such as fruit juice, food dyes or even sugar and salt, oils do not mix with water. The reason is related to the properties of oil and water. Water molecules are made up of one oxygen atom and two hydrogen atoms. In addition to having this very simple structure, water molecules are polar, which means there is an uneven distribution of charge across the water molecule. Water has a partial negative charge from its oxygen atom and partial positive charges on its hydrogen atoms. This polarity allows water molecules to form strong hydrogen bonds with each other, between the negatively charged oxygen atom on one water molecule and the positively charged hydrogen atoms of another. Other molecules such as salts and sugars are able to dissolve in water because of its polarity as well. The charges at either end of the water molecule help break up the chemical structures of other molecules.

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Oils, by contrast, are nonpolar, and as a result they’re not attracted to the polarity of water molecules. In fact, oils are hydrophobic, or “water fearing.” Instead of being attracted to water molecules, oil molecules are repelled by them. As a result, when you add oil to a cup of water the two don’t mix with each other. Because oil is less dense than water, it will always float on top of water, creating a surface layer of oil. You might have seen this on streets after a heavy rain—some water puddles will have a coating of oil floating on them.

In this activity we will test the power of surfactants to help us mix oil and water. The surfactant we will use is dish detergent, which helps break up the surface tension between oil and water because it is amphiphilic: partly polar and partly nonpolar. As a result, detergents can bind to both water and oil molecules. We’ll see the results of this property in this activity!

2 clear plastic water bottles with lids

2 cups of water

One-half cup of oil (olive, cooking or vegetable oils will all work)

Liquid dishwashing soap

Clock or timer

Permanent marker

Measuring cup

Measuring spoon

Food coloring (optional)

Preparation

Remove any labels from your water bottles.

Use your marker to label the bottles: Label the first “Oil+Water” and the second “Oil+Water+Soap.” Write the labels as close to the tops of the bottles as possible.

Pour one cup of water into each bottle.  

Carefully measure and pour one-quarter cup of oil into the bottle labeled Oil+Water. Allow the bottle to sit on a countertop or flat surface while you observe the water and oil. Does the oil sink to the bottom of the bottle, sit on top of the water or mix with it?

Repeat this step, adding one-quarter cup oil to the bottle labeled Oil+Water+Soap. Does the oil sink to the bottom, sit on top of the water or mix with it?

Carefully add three tablespoons of dish soap to the bottle labeled Oil+Water+Soap. Try not to shake the bottle as you add the dish soap.

Make sure the bottle caps are screwed on tightly to each bottle.

Holding a bottle in each hand, vigorously shake the bottles for 20 seconds.

Set the bottles down on a flat surface with plenty of light.

Note the time on your clock or set a timer for 10 minutes.

Observe the contents of each bottle. Hold them up to a light one at time so you can clearly see what is happening inside the bottle. Did anything change when you shook the bottles? Do the mixtures look the same in the both? If not, what is different between them? How would you explain the differences that you observe?

After 10 minutes have passed look at the contents of the bottles and note the changes. What does the oil and water look like in each bottle? Has the oil mixed with the water, sink to the bottom or rise to the top?

Extra:  Add food coloring to the water to get a lava lamp effect

Extra:  Test other types of soap, such as toothpaste, hand soap and shampoo by mixing them with oil and water. 

Observations and results In this activity you combined oil and water then observed how adding dish detergent changed the properties of this mixture. First you should have noticed that when you added the oil to the water they did not mix together. Instead the oil created a layer on the surface of the water. This is because oil is less dense than water and therefore it floats to the surface. When you shook the Oil+Water bottle you might have noticed the oil broke up into tiny beads. These beads, however, did not mix with the water. After you let the Oil+Water bottle sit for 10 minutes you should have observed the oil and water starting separating again almost immediately, and after another 10 minutes there was once again two distinct layers in your bottle.

In contrast you should have found shaking the Oil+Water+Soap bottle resulted in a lot of foam, but instead of immediately starting to separate, the mixture was a cloudy, yellow color. Eventually the oil and water should have separated into two layers again, but these layers should have appeared less distinct and cloudier than the layers in your Oil+Water bottle.

The difference between the two bottles results from adding dish detergent to the Oil+Water+Soap bottle. The detergent molecules can form bonds with both water and oil molecules. Therefore, although the oil and water aren’t technically mixing with each other, the dish detergent molecules are acting as a bridge between oil and water molecules. As a result, the oil and water molecules aren’t clearly separated in the bottle. Instead, you see a cloudy mixture, resulting from the oil, soap and water chains you’ve created by adding dish detergent.

More to explore Goo-Be-Gone: Cleaning Up Oil Spills , from Science Buddies Make Your Own Lava Lamp , from Scientific American The Chemistry of Clean: Make Your Own Soap to Study Soap Synthesis , from Science Buddies Science Activities for All Ages! , from Science Buddies

This activity brought to you in partnership with Science Buddies

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Origin of water on Earth

Water is a fundamental and indispensable component of Earth, playing a crucial role in the sustenance of life and the functioning of various geological and ecological processes. The presence of water on our planet has fascinated scientists and researchers for centuries, leading to numerous studies and theories aimed at unraveling the mysteries of its origin. Understanding the source of Earth’s water is not only a scientific pursuit but also holds implications for our understanding of the broader processes that shaped the early solar system.

Importance of water on Earth:

Water is essential for life as we know it. Its unique properties, such as high heat capacity, excellent solvent capabilities, and the ability to exist in three states (solid, liquid, and gas), make it a key player in various Earthly processes. It is a vital component for biological organisms, serving as a medium for biochemical reactions and a habitat for countless species. Additionally, water regulates temperature, shapes landscapes through erosion and weathering , and influences climate patterns.

The human dependence on water goes beyond basic survival, extending to agriculture, industry, and energy production. The availability of water resources has historically influenced the development and distribution of civilizations. Therefore, the study of the origin of Earth’s water is not only a scientific inquiry but also holds practical implications for managing and sustaining life on our planet.

Historical interest in understanding the origin of water:

The quest to understand the origin of Earth’s water has a long history, with various cultures and scientific traditions contributing to this intellectual pursuit. In ancient times, myths and creation stories often incorporated water as a primordial element, emphasizing its significance in the formation of the world.

In the modern era, scientific curiosity about the origin of water gained momentum as researchers began to explore the composition of celestial bodies and the conditions prevailing in the early solar system. Theories about water delivery mechanisms, such as cometary impacts and contributions from asteroids, emerged as scientists sought to explain the presence of water on Earth.

Advancements in planetary science, astronomy, and geochemistry have allowed researchers to investigate the isotopic composition of Earth’s water and compare it with that of potential extraterrestrial sources. This interdisciplinary approach has provided valuable insights into the likely sources and processes that contributed to the abundance of water on our planet.

In summary, the origin of water on Earth is a topic of enduring scientific interest with implications for our understanding of the planet’s history, the development of life, and the broader processes shaping our solar system. The ongoing quest to unravel the mysteries of Earth’s water continues to drive research and exploration, bringing together diverse fields of study in a collaborative effort to unlock the secrets of our planet’s liquid lifeblood.

The Formation of the Solar System

Late heavy bombardment hypothesis, outgassing from the earth’s interior, the role of comets and asteroids, summary of key points.

Overview of the Early Solar System:

The solar system formed approximately 4.6 billion years ago from a vast, rotating cloud of gas and dust known as the solar nebula. This cloud collapsed under the influence of gravity, leading to the formation of the Sun and the surrounding planetary system. The early solar system was a dynamic environment characterized by intense heat, radiation, and the presence of various particles and materials.

Formation of the Sun and Protoplanetary Disk:

As the solar nebula collapsed, the majority of its mass gathered at the center, forming the Sun. The rest of the material flattened into a spinning disk, known as the protoplanetary disk, surrounding the young Sun. This disk consisted of gas and dust particles, including elements like hydrogen, helium, and heavier elements produced by previous generations of stars.

Within the protoplanetary disk, collisions and gravitational interactions between particles led to the formation of larger clumps of matter, known as planetesimals. The intense heat from the young Sun caused the inner regions of the disk to be predominantly composed of rocky materials and metals, while the outer regions contained more volatile compounds in icy form.

Development of Planetesimals and Protoplanets:

Planetesimals are small, solid bodies ranging in size from a few meters to hundreds of kilometers. Over time, these planetesimals continued to collide and merge, forming even larger objects known as protoplanets. The gravitational interactions between protoplanets further facilitated the growth process, leading to the formation of planetary embryos.

As the protoplanets continued to accrete material from the protoplanetary disk, they also began to clear their orbits of debris. This process marked the transition from protoplanets to planets. The planets in our solar system can be broadly categorized into two groups based on their compositions and characteristics:

• Terrestrial Planets: The inner planets, including Mercury, Venus, Earth, and Mars, are characterized by their rocky compositions and relatively smaller sizes.
• Jovian Planets (Gas Giants): The outer planets, Jupiter, Saturn, Uranus, and Neptune, are significantly larger and primarily composed of lighter elements, such as hydrogen and helium. These planets also have extensive systems of rings and numerous moons.

The formation of the solar system involved intricate processes of gravitational attraction, collisions, and the redistribution of materials within the protoplanetary disk. The remnants of this dynamic era can still be observed in the diverse characteristics of the planets and other celestial bodies that make up our solar system today. The study of these early processes provides crucial insights into the formation and evolution of planetary systems in the universe.

The Late Heavy Bombardment (LHB) is a theoretical event that is believed to have occurred approximately 3.8 to 4.1 billion years ago during the early stages of the solar system’s history. This period was characterized by a sudden increase in the rate of impact events, particularly involving comets and asteroids, on the inner planets, including Earth, Moon, Mars, and Mercury. The Late Heavy Bombardment hypothesis suggests that these celestial bodies experienced a significant influx of impactors, causing widespread cratering and shaping the surfaces of these planets and moons.

Explanation of the Late Heavy Bombardment:

The exact cause of the Late Heavy Bombardment is still a topic of scientific investigation and debate. One leading hypothesis is that gravitational interactions among the giant planets, particularly Jupiter and Saturn, caused a rearrangement of their orbits. This gravitational disturbance led to the scattering of comets and asteroids from the outer regions of the solar system, sending them on trajectories that intersected with the inner planets.

As a result, a barrage of these objects collided with the surfaces of the inner planets, causing intense cratering and altering the topography of these bodies. The Late Heavy Bombardment is considered a crucial phase in the solar system’s history, influencing the evolution of planetary surfaces and potentially impacting the development of early life on Earth.

Role of Comets and Asteroids:

Comets and asteroids played a central role in the Late Heavy Bombardment. Comets are icy bodies composed of water, frozen gases, dust, and other volatile compounds, while asteroids are rocky or metallic bodies. The impact of comets and asteroids during the Late Heavy Bombardment had several significant effects:

• Cratering and Surface Modifications: The impacts of these celestial bodies caused widespread cratering on planetary surfaces. The Moon, for example, preserves a record of this intense bombardment in the form of impact craters.
• Delivery of Volatiles: Comets are rich in volatile compounds, including water ice. The impacts of comets could have contributed to the delivery of water and other volatile substances to the inner planets, including Earth.

Delivery of Water to Earth During Impacts:

The impact of comets during the Late Heavy Bombardment is believed to have played a crucial role in bringing water to Earth. The early Earth was likely a hot and dry environment, and the delivery of water-rich comets provided a source of water that eventually contributed to the formation of Earth’s oceans.

The water delivered by comets during impact events would have vaporized upon collision but subsequently condensed and accumulated on the planet’s surface as it cooled. This process is thought to be one of the mechanisms by which Earth acquired its water, influencing the development of the conditions necessary for life.

In summary, the Late Heavy Bombardment was a period of intense asteroid and comet impacts that significantly shaped the surfaces of the inner planets, including Earth. The delivery of water by comets during this bombardment is a key aspect of the hypothesis, providing insights into the origin of Earth’s water and the broader dynamics of the early solar system.

Overview of Volcanic Activity:

Volcanic activity is a geologic process involving the release of magma (molten rock), gases, and other materials from the Earth’s interior to its surface. This process is associated with volcanic eruptions, which can take various forms, including explosive eruptions with ash clouds, lava flows, and more gradual effusive eruptions. Volcanoes are the primary geological features through which volcanic activity is manifested.

Volcanic activity occurs at plate boundaries and hotspots, where tectonic plates interact. There are three main types of plate boundaries where volcanic activity is commonly observed:

• Divergent Boundaries: Plates move away from each other, creating gaps in the Earth’s crust. Magma rises to fill these gaps, leading to the formation of new crust.
• Convergent Boundaries: Plates collide, with one being forced beneath the other in a process known as subduction. This can lead to the melting of the subducted plate and the generation of magma that rises to the surface, resulting in volcanic arcs.
• Hotspots: These are areas where magma rises from deep within the mantle, creating localized volcanic activity. Hotspots can occur away from plate boundaries and often create island chains.

Release of Gases from the Earth’s Mantle:

The Earth’s mantle, located beneath the crust, is a semi-solid layer composed of rock and minerals . Volcanic activity provides a pathway for gases trapped in the mantle to reach the surface. The most common gases released during volcanic eruptions include:

• Water Vapor (H2O): Water is a major component of volcanic gases and is released both in the form of steam and as dissolved water in magma.
• Carbon Dioxide (CO2): This greenhouse gas is released during volcanic eruptions and contributes to the carbon cycle.
• Sulfur Dioxide (SO2): Volcanic emissions of sulfur dioxide can lead to the formation of sulfate aerosols in the atmosphere, affecting climate and air quality.
• Other Gases: Volcanic gases may also include nitrogen, methane, hydrogen, and trace amounts of other compounds.

Contribution of Water Vapor to the Atmosphere:

Water vapor released during volcanic eruptions is a significant contributor to the Earth’s atmosphere. The water vapor released from the mantle can have several effects:

• Climate Impact: Water vapor is a greenhouse gas, and its release during volcanic activity can contribute to short-term climate effects. However, the overall impact depends on the scale and duration of the eruption.
• Formation of Clouds: Water vapor released during volcanic eruptions can condense in the atmosphere, forming clouds. These volcanic clouds may have both local and global effects on weather patterns.
• Water Source for Oceans: Over geological timescales, the continuous outgassing of water vapor from volcanic activity has contributed to the formation and replenishment of Earth’s oceans. Water released during volcanic eruptions eventually condenses and falls as precipitation.

While the delivery of water to the Earth’s surface through volcanic outgassing is an ongoing process, the Late Heavy Bombardment, as discussed earlier, is also considered a significant contributor to the Earth’s water content, bringing water-rich comets to the planet. Together, these processes have shaped the Earth’s atmosphere and surface over billions of years.

Composition of Comets and Asteroids:

Comets and asteroids are celestial bodies that played a crucial role in the early solar system and continue to influence the dynamics of planets, including Earth.

Comets: Comets are icy bodies composed of volatile compounds, water ice, dust, and other organic molecules. The nucleus of a comet is a solid, icy core that can range in size from a few kilometers to tens of kilometers. As a comet approaches the Sun, solar radiation causes the volatile materials to sublimate, creating a glowing coma (a cloud of gas and dust) and often a tail that points away from the Sun. The composition of comets includes water ice, carbon dioxide, methane, ammonia, and complex organic molecules.

Asteroids: Asteroids are rocky or metallic bodies that vary in size from a few meters to hundreds of kilometers. They are remnants from the early solar system and are primarily composed of minerals, metals, and rocky materials. Asteroids are found in the asteroid belt between Mars and Jupiter, but they can also be present in other regions of the solar system.

Evidence Supporting Their Contribution to Earth’s Water:

• The isotopic composition of Earth’s water, particularly the ratio of deuterium to hydrogen (D/H ratio), has been studied. Cometary water is often found to have a D/H ratio that matches the values observed in Earth’s oceans, supporting the idea that comets could have been a source of Earth’s water.
• The late stages of the solar system’s formation involved dynamic processes, such as the migration of giant planets and the Late Heavy Bombardment. These processes could have scattered comets and asteroids towards the inner solar system, leading to impacts on Earth and the delivery of water.
• Space missions, such as the European Space Agency’s Rosetta mission to comet 67P/Churyumov–Gerasimenko, have provided direct observations of water ice on comets. Additionally, analysis of meteorites, which are remnants of asteroids, has revealed the presence of hydrated minerals, suggesting that asteroids may contain water.

Models of Water Delivery from Celestial Bodies:

• This model suggests that during the Late Heavy Bombardment, comets impacted the Earth, delivering water and volatile compounds. The heat generated during impact would have caused the water in the comets to vaporize and contribute to the formation of Earth’s oceans.
• Asteroids, particularly carbonaceous chondrites, are known to contain water-bearing minerals. It’s proposed that asteroids, through impacts, released water into the Earth’s atmosphere. The water vapor could have then condensed and formed oceans over time.
• Some models propose a combination of cometary and asteroidal contributions to Earth’s water. The diverse compositions of comets and asteroids could account for variations in isotopic ratios observed in Earth’s water.

The exact contribution of comets and asteroids to Earth’s water is still an active area of research, and ongoing space missions and studies of celestial bodies continue to provide valuable insights into the early history of our solar system and the origin of water on Earth.

• Earth’s water likely has multiple sources, including comets and asteroids, as well as outgassing from the Earth’s interior during volcanic activity.
• The Late Heavy Bombardment hypothesis suggests that cometary impacts during a specific period significantly contributed to Earth’s water content.
• Volcanic activity releases gases, including water vapor, from the Earth’s mantle to the surface.
• This process not only shapes the Earth’s landscape but also contributes to the composition of the atmosphere and the formation of oceans.
• Comets are icy bodies composed of water ice, volatile compounds, and organic molecules.
• Asteroids are rocky or metallic bodies primarily made up of minerals, metals, and rocky materials.
• The isotopic composition of Earth’s water, as well as observations of comets and asteroids, supports the idea that these celestial bodies played a role in delivering water to Earth.
• Cometary impacts and asteroidal contributions, particularly during the Late Heavy Bombardment, are considered significant mechanisms for water delivery.
• The cometary impact model suggests that comets delivered water to Earth during collisions, while the asteroidal contribution model proposes that asteroids, through impacts, released water into the Earth’s atmosphere.
• Some models consider a combination of cometary and asteroidal contributions to explain the diversity in isotopic ratios observed in Earth’s water.

Significance of Understanding the Origin of Water on Earth:

• Fundamental for Life: Water is essential for life as we know it. Understanding its origin provides insights into the conditions necessary for life to emerge and thrive on Earth.
• Earth’s Geological History: Studying the origin of water contributes to our understanding of Earth’s geological history, including processes like volcanic activity and the Late Heavy Bombardment.
• Planetary Formation: Insights into the origin of Earth’s water contribute to our broader understanding of planetary formation and the distribution of water in the solar system.

Implications for the Search for Water on Other Planets:

• Habitability Assessment: Understanding the mechanisms of water delivery to Earth informs the search for water on other planets. It helps in assessing the potential habitability of these planets and moons.
• Exoplanet Studies: The study of water origins on Earth guides the search for water in exoplanetary systems. It provides criteria for assessing the habitability of exoplanets based on their water content.
• Astrobiology: Knowledge of water’s origin is crucial for astrobiology, guiding the search for environments that may support life beyond Earth. Water is a key factor in the habitability of celestial bodies.

In conclusion, unraveling the origin of water on Earth is not only a fascinating scientific inquiry about our planet’s history but also has broader implications for understanding planetary formation, habitability, and the potential for life in the universe. The lessons learned from Earth’s water story contribute to the ongoing exploration of other celestial bodies and the search for life beyond our own planet.

• Morbidelli, A., et al. (2000). “Source regions and timescales for the delivery of water to the Earth.” Meteoritics & Planetary Science.
• Gomes, R., et al. (2005). “Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets.” Nature.
• Marty, B., and Tolstikhin, I. N. (1998). “CO2 fluxes from mid-ocean ridges, arcs and plumes.” Chemical Geology.
• Cochran, A. L. (2009). “Comets.” Annual Review of Astronomy and Astrophysics.
• DeMeo, F. E., and Carry, B. (2014). “The taxonomic distribution of asteroids from multi-filter all-sky photometric surveys.” Icarus.
• Altwegg, K., et al. (2015). “67P/Churyumov–Gerasimenko, a Jupiter family comet with a high D/H ratio.” Science.
• Greenwood, J. P., et al. (2011). “Hydrogen isotope ratios in lunar rocks indicate delivery of cometary water to the Moon.” Nature Geoscience.
• Lunine, J. I. (2005). “The Atmospheres of Earth and the Planets.” Annual Review of Earth and Planetary Sciences.
• Wordsworth, R., and Pierrehumbert, R. T. (2014). “Abiotic oxygen-dominated atmospheres on terrestrial habitable zone planets.” The Astrophysical Journal.

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Walking Water Rainbow Science Experiment

Let’s make a walking water rainbow! There’s no better way for little scientists to learn about capillary action and color mixing than by making water walk (yes – walk!) in this colorful rainbow science experiment. This science experiment is a favorite of ours because it’s so easy to set up and the results are almost immediate.

Check out the simple step-by-step below and then gra b 30 more jaw-dropping (but easy prep!) science experiments kids will love from our shop!

Getting Ready

To prep, I gathered our supplies:

• 6 wide-mouth glasses or jars
• Paper towels (use the kind where you can select a size)
• Food dye or liquid water colors (red, yellow, and blue)

I grabbed the six small glasses first .  We’ve had success using wide-mouth drinking cups and canning jars, too.  Even though they all worked, just remember that bigger glasses will need more food coloring.

I ripped off six sheets of paper towel and folded each sheet in thirds, lengthwise.

We were using pretty small glasses, so I cut a few inches off the folded paper towel so it would fit in the glasses.

It’s a good idea to test your paper towel strip to make sure they fit properly in your glasses.  They should be able to go from the bottom of one jar to the next without sticking up in the air too much. The paper towel on the left shows the just-right height.  It’s important to set up this rainbow science experiment for success!

Making a Rainbow

This colorful rainbow science experiment is so simple and quick, it’s perfect for even the youngest little scientists.  My 3 year old, Q, couldn’t wait to get started.

First, I had him line up the glasses and fill the first one with a good squirt of red watercolor , the third with yellow, and the fifth glass with blue.  We left the other glasses empty.

Next, I helped Q add water to the glasses with color until the colored water almost reached the top.

We moved the glasses into a circle and added the paper towels .  Starting with the red, we added one end of the paper towel and then put the other end in the empty glass next to it.

We continued around until the last paper towel was placed into the red glass.

We saw the color wick up the paper towel right away.  This rainbow science experiment doesn’t take long to get going!

After another several minutes, the colored water had almost travelled the whole length of each paper towel.

Five minutes later, the water had traveled all the way up and then down the paper towel and was dripping into the empty glass.

The yellow and red water dripped into the empty cup to make orange!  It made for a good lesson on color mixing.

After another five minutes, we could see the water level had dropped in the red, yellow, and blue glasses and rose in the once empty glasses as the water continued to travel from the more full glasses to the less full glasses.

We grabbed a snack and watched our beautiful rainbow science experiment during the next 20 minutes. The water continued to walk from the primary colored glasses to fill the secondary-colored glasses until all the jars were filled equally.

Not Working?

If you aren’t seeing much movement within a few minutes, it may be that you need to add more water to your colored water glasses.  It really needs to be almost at the top for the water to walk quickly.  So try topping off those glasses and seeing if that gets things moving.

If you see the water moving up the paper towel but it seems like it’s taking forever , it may be the type of paper towel you are using.  You want a paper towel that will really hold a lot of water.  We have used Bounty Select-a-Size and Target’s Up and Up Brand Select-a-Size with success.

It really is worth the extra effort of trying different cups and paper towels to get this activity to work.  And once you have had success, don’t throw out those beautifully-colored paper towels or the colored water!  We gently squeezed out our paper towels and let them dry in a heap on a baking sheet.  We ended up with gorgeous tie-dyed looking paper towels to use for crafts and we used the leftover water as watercolors for painting with later.

The Science Behind It

This rainbow science experiment is as magic as the science behind it.  The colored water travels up the paper towel by a process called capillary action . Capillary action is the ability of a liquid to flow upward, against gravity, in narrow spaces.  This is the same thing that helps water climb from a plant’s roots to the leaves in the tree tops.

Paper towels, and all paper products, are made from fibers found in plants called cellulose .  In this demonstration, the water flowed upwards through the tiny gaps between the cellulose fibers.  The gaps in the towel acted like capillary tubes, pulling the water upwards.

The water is able to defy gravity as it travels upward due to the attractive forces between the water and the cellulose fibers.

The water molecules tend to cling to the cellulose fibers in the paper towel.  This is called adhesion .

The water molecules are also attracted to each other and stick close together, a process called cohesion .  So, as the water slowly moves up the tiny gaps in the paper towel fibers, the cohesive forces help to draw more water upwards.

At some point, the adhesive forces between the water and cellulose and the cohesive forces between the water molecules will be overcome by the gravitational forces on the weight of the water in the paper towel.  

When that happens, the water will not travel up the paper towel anymore. That is why it helps to shorten the length that colored water has to travel by making sure your paper towel isn’t too tall and making sure you fill your colored liquid to the top of the glass.

Rainbow Science Activity Extensions

Turn this demonstration into a true experiment by varying the water level (volume) you start with and seeing how long it takes the water to reach the empty glass.

Or start with the same volume of colored water and change the brand, type (single vs double ply, quilted vs not) or length of paper towel to see how long it takes for the water to “walk” to the empty glass.

You could even use the same volume of water, same length and brand of paper towel but vary the height of the filled glass , by raising them up on books, to see how that affects the speed of the water as it “walks” to the empty glass.

Have you had enough fun with the paper towels?  Try using other paper products to see how the type of paper effects the results.  Try toilet paper, printer paper, newspaper or a page from a glossy magazine.  What do you predict will happen?

Grab a Record Sheet

Help kids keep track of their results by grabbing our free record sheet! Then grab 30 more jaw-dropping (but easy prep!) science experiments kids will love from our shop!

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Investigation: Properties of Water with Stats

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All life depends upon the unique features of water which result from its polar nature and ‘stickiness.’ Some of the unique properties of water that allow life to exist are:

It is less dense as a solid than as a liquid (ice floats)

It sticks to itself – cohesion – cohesion is also related to surface tension.

It sticks to other polar or charged molecules – adhesion – adhesion results in phenomena such as capillary action.

It is a great solvent for other polar or charged molecules.

It has a very high specific heat – it can absorb a great deal of heat energy without increasing in temperature

It has a neutral pH of 7, which means the concentrations of H+ and OH- ions are equal.

Introduction to Statistics:

Statistical analysis is used to collect a sample size of data which can infer what is occurring in the general population . Standard deviation (often reported as +/-) shows how much variation there is from the average (mean). 

If data points are close together, the standard deviation with be small . If data points are spread out , the standard deviation will be larger. Typical data will show a normal distribution (bell-shaped curve). In normal distribution, about 68% of values are within one standard deviation of the mean, 95% of values are within two standard deviations of  the mean, and 99% of the values are within three standard deviations of the mean x̄ .       

 The formula for standard deviation is shown to the below, where     is the mean, xi is any given data value, and n is the sample size. Consider the following sample problem.

Quickcheck :  On a normal distribution curve, what percentage of data points will be within 1 standard deviation of the mean?  ___________ How many will be within 2 standard deviations of the mean? __________        

Step 1 : Find the Mean (x̄) . _____________

Step 2 : Determine the Deviation (x i - x̄ ) 2 from the mean for each value and square it, then add up all of the  total values.                          

Step 3 : Calculate the Degrees of Freedom (n-1) . ______________

Step 4 : Put it all together to find s . _______________ 

Step 5 :  Determine the data range for one standard deviation : _________________  two standard deviations : _________________

Using the data from the standard deviation example above, the mean is 84 and the standard deviation  is 9. What is the SE?  _____

Notice that in the last image, the error bars tell us that we can be 95% confident (2 SEM) that the number of acorns collected at Worthen School is significantly different from the Wilson Park and Horseshoe Lake sites.  Things are not as clear-cut between Wilson Park and Horseshoe Lake because the error bars overlap. 

Pre-Lab Questions: Use the above background information and your textbook to answer the following questions.

1. Why is water considered to be polar?

2. Sketch a molecule of water (include the partial charges).

3. Which type of bonds form between the oxygen and hydrogen atoms of TWO DIFFERENT water molecules?

4. Which type of bonds form between the oxygen and hydrogen atoms of WITHIN a water molecule?

5. Explain what shorter error bars mean when you are analyzing data from a graph.

Hypothesis:

Materials : Penny, water, soap, pipette, paper towel, 70% rubbing alcohol

Procedure :

Obtain a DRY penny and place it on a DRY paper towel. 

Using a clean pipette, add water to the penny drop by drop until it overflows. Be sure to count the drops! Record the number of drops for Trial 1 in Data Table 1 below. 

Repeat steps 1-2 for a total of five trials. 

Place 1 ml of soap in 50 ml of water to create a solution.  Test this number of drops of the soap and water can fit onto the penny.

Repeat the experiment using 70% rubbing alcohol.  You do not need to dilute it with water, it is already diluted.

Data Collection:

Data Table 1: Number of Drops of Distilled Water Contained on the Surface of a Penny

Data Table 2: Statistical Analysis of the Number of Drops of Distilled Water Contained on the Surface of a Penny

Create an appropriately labeled bar graph to illustrate the sample means for the penny within 95% confidence (+/- 2 SEM). Don’t forget a title that includes the independent and dependent variables and axes labels with units. 

1. Make a Claim about how soap and alcohol affects hydrogen bonds between water molecules.  This can be written as two separate claims. 

2. Using data from this experiment, provide Evidence from your investigation that supports the claim(s).  

3. Using background knowledge and data from this lab, provide Reasoning that uses the evidence to justify the claim and comment on how confident you are in your conclusions. Here, you may want to include deductive reasoning that uses the properties of water to explain why you obtained the results. 

4. Suggest another experiment that you could perform that deals with surface tension. Write your question/ hypothesis below and a brief description of how you would conduct the experiment.

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Science Experiments

Glowing Water Science Experiment

Do you have any predictions? With three bottles of water, one bottle filled with water mixed with highlighter dye, one bottle filled with tonic water, and one bottle filled with regular tap water, which ones do you think will glow?

Borrow a black light, get your supplies together, and give this simple and fun science experiment a try! We have a supplies list, printable instructions as well as a demonstration video with experiment explanation below. Explore phosphors and have fun while learning!

JUMP TO SECTION:   Instructions  |  Video Tutorial  |  How it Works | Purchase Lab Kit

Supplies Needed

• 3 Empty Bottles or Drinking Glasses
• Highlighter
• Tonic Water
• Black light

Glowing Water Science Lab Kit – Only $5

Use our easy Glowing Water Science Lab Kit to grab your students’ attention without the stress of planning!

It’s everything you need to  make science easy for teachers and fun for students  — using inexpensive materials you probably already have in your storage closet!

Glowing Water Science Experiment Instructions

Step 1 – Prepare the water for the first bottle. To do so, pull the back off a highlighter and drop the ink into a cup of water. Set aside.

Step 2 – Prepare the water for the second bottle. Do this by filling the second bottle with tonic water.

Helpful Tip: If you buy tonic water that is already is a clear glass jar, you can just use that.

Step 3 – Prepare the water for the third bottle. Do this by filling the third bottle with regular tap water.

Step 4 – Take the water with the highlighter ink in it that you prepared in step one. Sir the water to mix in the ink and then pour it into the first bottle.

Step 5 – Position the black light behind the bottles.

Step 6 – Turn on the black light and observe the three bottles. Do any of them glow? Do you know why? Find out the answer in the how does this experiment work section below.

Video Tutorial

How Does the Science Experiment Work

The bottle with regular tap water does not glow when placed near a black light.

The bottle with water and highlighter dye and the bottle with tonic water do glow when placed near a black light. This is because highlighter dye and a chemical found in tonic water called quinine contain something called phosphors. Phosphors are substances that emit light (or luminesce) when exposed to radiation like UV light. When you shine a UV light on phosphors, the phosphors become “excited” and glow. Your teeth and fingernails also contain phosphors so they will also glow in UV light!

I hope you enjoyed the experiment. Here are some printable instructions:

Instructions

• Prepare the water for the first bottle. To do so, pull the back off a highlighter and drop the ink into a cup of water. Set aside
• Prepare the water for the second bottle. Do this by filling the second bottle with tonic water. Tip: If you buy tonic water that is already is a clear glass jar, you can just use that.
• Prepare the water for the third bottle. Do this by filling the third bottle with regular tap water.
• Take the water with the highlighter ink in it that you prepared in step one. Sir the water to mix in the ink and then pour it into the first bottle.
• Position the black light behind the bottles.
• Turn on the black light and observe the three bottles. Do any of them glow? Do you know why?

Reader Interactions

April 7, 2017 at 1:21 pm

where do you get tonic water besides online

October 18, 2017 at 8:54 pm

At the store

October 22, 2017 at 9:43 pm

A liquor store

January 31, 2018 at 10:32 pm

HEB or any grocery store near beer/ liquor isle.

April 9, 2018 at 5:45 pm

In wallmart

January 9, 2020 at 6:29 pm

I all was get my tonic water at wallmart.

January 19, 2019 at 11:53 am

Where do you get a black light and tonic water instead online? I love how you did it! Next year, for my science project I will do it.

January 23, 2020 at 9:31 pm

Both at Walmart

May 30, 2019 at 6:13 pm

My daughter did this experiment at school, yesterday. It was a big hit. I’d add the pic the teacher sent, if I knew how.

January 9, 2020 at 6:34 pm

Where do you get a black light and tonic water instead online?I love how you did it!Next year,for my science project I will do it.

March 12, 2020 at 5:01 pm

cool experiment

February 22, 2022 at 11:39 am

My friend and I are doing this experiment for our science fair project we just found it online. We cannot wait to do it!!! This is the first time we ever choose this!!!!

February 6, 2024 at 1:28 pm

I like this and I will do it for my 4th grade science project instead of forming neurons for a robot.

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7 Types of Bottled Water

Water, water, everywhere. is one variety healthier than others.

Andrea Wickstrom,

Standing in front of the water aisle in stores can feel overwhelming. Once we filled our glasses with the simplest drink that just flowed from the tap, but now the choices are dizzying: vitamin water, hydrogen water, sparkling water, electrolyte water.

Americans spent an estimated $49 billion in 2023 on bottled water and drank about 16 billion gallons , according to the Beverage Marketing Corp. That’s a lot of bottled-up H2O.

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Though it’s true that staying hydrated is crucial to overall health — and many older adults are dehydrated — it’s not clear whether spending extra money on something that’s included in your monthly water bill can make you any healthier.

How are all the drinking water choices different, and is one better than another?

In general, the United States has some of the world’s safest drinking water. Some U.S. water is safe to drink directly from the source, while water from other sources must be treated before consumption because of potential chemical and bacterial contamination.

On April 10, the Biden administration finalized limits on “forever chemicals” in drinking water, requiring utilities to reduce them to the lowest level that can be reliably measured. Government officials say these chemicals, called PFAS (polyfluoroalkyl substances), are linked to liver disease, heart disease and certain cancers. The administration has also proposed rules that would require cities to replace lead water pipes within 10 years.

An estimated 43 million Americans receive water from a private underground well. Well water can be cloudy, have a rotten egg odor from hydrogen sulfide, and leave rust stains. This water is not regulated, so homeowners are responsible for ensuring their supply is safe for drinking, usually through recommended annual testing.

Hard Water Vs. Soft Water

Many households have soft water, but it isn’t a requirement. A water softener removes the water’s hardness, caused by calcium and magnesium, and replaces it with sodium.

Some may wonder if their soft water tastes salty. Some sources say that’s a myth; others say people with very discerning taste buds may notice it.

The amount of sodium in one 8-ounce glass of softened water is about 12.5 milligrams (the recommended daily intake is 2,300 mg). Soft water is safe for the general public, but those with strict low-sodium diets may need their doctor’s guidance on water selection.

To avoid drinking soft water, you can switch to a nonsalt-based softening system (using potassium instead) or add a reverse osmosis system to your kitchen supply. Other solutions include having the water softener hooked up to your hot water to reserve for laundry, bathing and cleaning.

Other than private well water, the U.S. Environmental Protection Agency (EPA) regulates and monitors public water supply and tests and treats the water.

Water that doesn’t taste or smell good may be confused with water that is not good for you. A safe amount of chlorine kills bacteria and viruses and keeps water pipes clean, but it doesn’t taste good. Chlorine can be removed with a filter.

“Water can sometimes have a bad smell, taste or appearance, but these features don’t usually last long or indicate a public health concern,” says registered dietitian Kourtney Johnson. “Chlorine, chemicals or a medicine-like taste or smell don’t typically mean there’s an immediate health threat.”

Tap water that doesn’t taste or smell good, as well as news reports of problems with the water coming from our faucets, may explain in part why millions of Americans turn to bottled water.

Bottled water

The U.S. Food and Drug Administration (FDA) strictly regulates bottled water production and distribution. The FDA has set out Current Good Manufacturing Practices (CGMPs) that require bottled water companies to maintain sanitary conditions throughout manufacturing and transportation, protect the approved water sources and test the final product.

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Some sparkling waters, seltzer waters, tonics and club soda aren’t included as bottled water under FDA regulations. They are considered soft drinks.

Although experts say bottled water is generally safe, there are a few concerns.

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Filtered water may remove fluoride, which is safe to drink and helps prevent tooth decay. Sometimes, manufacturers will reintroduce minerals after purification.

Microplastics are substances used to give plastic bottles transparency, shape and flexibility. A possible link between plastics and disruption of the endocrine system and thyroid is under investigation.

“Growing evidence shows that microplastics negatively affect the endocrine, reproductive and immune systems, as well as bacteria found in the gut. The thyroid plays a role in regulating almost all organs in the body, and long-term exposure to plastics negatively affects its ability to regulate growth, development, metabolism and reproduction,” Johnson says.

Water Filters

Options to enhance the condition of your home’s well or tap water include:

• A whole house filtration system. 
• A filtered refrigerator water dispenser.
• A filtered countertop water pitcher or faucet attachment.
• A reverse osmosis system.

Here’s a breakdown on seven popular varieties of bottled water.

1. Spring water

Spring water originates from rainwater that moves underground and is filtered naturally by rock and minerals. After it is pushed up to the ground’s surface, the water is collected in springs. Per FDA regulations, when manufacturers bottle and sell it, it must have the same composition and quality as the spring water at its source.

The amount of minerals in spring water isn’t substantial, so it doesn’t provide additional health benefits compared with other water. However, many people enjoy the taste.

2. Mineral water

To be labeled mineral water, this type of bottled water must contain at least 250 parts per million total dissolved solids. It differs from other types of bottled water due to minerals and trace elements that are present at the water source. Minerals cannot be added later, according to FDA rules.

3. Alkaline water 

Multiple brands manufacture alkaline water, which is altered to a higher pH. Alkaline water can be more expensive than other bottled water, but studies have yet to prove its health benefits. Some claim it can neutralize acid in the bloodstream, give better workout recovery and help prevent disease. A 2021 Iranian study found it may improve bone density in postmenopausal women with osteoporosis. The science on these claims is limited, and studies are generally small or in animals, not humans. Larger studies are needed to evaluate any potential health benefits.

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“The body does an incredible job at keeping our pH within a very tight and controlled range. Consuming more alkaline water will not shift your pH outside of its normal range,” says Jen Hernandez, a registered dietitian who specializes in helping people with kidney disease.

Some suggest drinking alkaline water may help those who suffer from acid reflux, but Hernandez is skeptical.

“Adding this type of water into a very acidic environment, like the stomach, which is supposed to be producing acid to help us with digestion and breaking down foods, is almost counterintuitive,” Hernandez says.

4. Water with vitamins

Some manufacturers enhance water with vitamins. This water usually comes in sugar-sweetened and sugar-free options. In some brands, a 20-fluid-ounce bottle has up to 27 grams of added sugar (50–100 percent of the daily recommended limit), so those watching sugar content should check labels. Sugar-free options use stevia, monk fruit or artificial sweeteners.

Vitamin-infused waters may contain more than 100 percent of the daily recommended value of vitamins B and C. These are water-soluble vitamins, meaning that the kidneys will excrete any excess in your urine.

“So you’re just going to pay for expensive urine at that point. ... Your body is going to say, ‘I don't need this quantity,’ ” Hernandez says. “It is ideal to get our vitamins from foods as they provide many other benefits and nutrients.”

5. Electrolyte water

Sports drinks are intended for athletes who lose a lot of fluid and electrolytes through sweat. Such drinks often aren’t necessary for moderate exercisers or sedentary people. Electrolyte water may be beneficial short-term under certain circumstances, such as when people are exercising for long periods, have prolonged exposure to heat or are ill with vomiting and diarrhea. Experts say regular water is usually sufficient for meeting moderate exercise hydration needs.

6. Hydrogen water

Hydrogen water is plain water with hydrogen gas added to it. The water can be bought with the hydrogen in it, or people can purchase hydrogen tablets to add to water at home.

Hydrogen water is gaining interest due to its potential health benefits. A 2024 review of studies found that it may have antioxidant and anti-inflammatory properties, as well as improve physical endurance. Most studies have been small, and research is mixed. Further rigorous research is needed to confirm any benefits.

7. Purified water

Plain bottled water is not merely tap water in a bottle, although some bottled water does come from municipal sources. To be labeled purified, the water goes into a production plant and through a process that can include distillation, deionization or reverse osmosis, according to the International Bottled Water Association . It is then sold in individual, sanitary, sealed containers.

Is one type better?

Most people get the electrolytes and minerals they need from food, not fluids. The amount in drinking water is relatively low and not enough to meet our dietary needs.

Is there a best daily drinking water? Some say the right water is the one you will drink. Many people enjoy the taste and convenience of bottled water and prefer it to tap water.

On the other hand, purified, highly regulated, readily available tap water is likely coming from your kitchen faucet. With additional home filters, cost-effective tap water is an excellent daily drinking choice, and there are no toxins from plastic bottles.

Having a pitcher of filtered tap water on the counter at home, in sight as a reminder, can be great for hydration needs, Hernandez says.

Andrea Wickstrom is a registered nurse who has covered health and medical topics as well as health-related news for multiple publications including Next Avenue, Nurse Journal, HeartValveSurgery.com and Healthnews.

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What This Scientist Says You Need to Know About Hundreds of Thousands of Plastic Particles in Your Drinking Water (Exclusive)

One of the researchers behind a pioneering new study on bottled water answers PEOPLE's questions about their investigation's unsettling findings

Johnny Dodd is a senior writer at PEOPLE, who focuses on human interest, crime and sports stories.

Amy Goldstein Photography

 In January Phoebe Stapleton, associate professor of pharmacology and toxicology at Rutgers University, co-authored a groundbreaking study that revealed the alarming amount of tiny plastic fragments — known as nanoplastics — found in bottled water .

Each liter of water contained an average of 240,000 particles from seven different types of plastics. Nearly 90 percent of these particles were nanoplastics made up of synthetic chemicals with potentially dangerous health effects, such as immune dysfunction and carcinogenicity; the remainder were larger microplastics.

PEOPLE speaks with Stapleton to get answers about the unsettling findings in this week's issue featuring our Earth Day Special .

How do these particles get into the water?

Stapleton: Of the three different brands of water we examined, the particles all came from the bottle and the cap. But with two of the brands, the highest concentrations were in the water before it got into the bottle. We haven’t done an analysis to test if it came from the source water or if it came from the filtering and processing.

What happens when these particles enter the body?

Stapleton: The body has a way to clear microsize particles, but the smaller (nano) particles are able to bypass those protections. For example, within 24 hours of these particles entering the gastrointestinal system, we were able to find them in maternal tissues (in animal test subjects) and in placenta and fetal tissues .

For more of our Earth Day Special, pick up the latest issue of PEOPLE, on newsstands Friday, or subscribe here .

What’s the difference between microplastics and nanoplastics?

Stapleton: A microplastic is anywhere between one micron and five millimeters in size. That’s about the size of a grain of sand, a grain of salt, a sesame seed. It’s something you can see, but just barely. Nanoparticles are about a thousand times smaller than the smallest micro particle. They’re invisible to the naked eye and in the bacteria and virus size range.

University of Texas at Austin

What’s the most troubling aspect of this study?

Stapleton: One concerning question is where exactly in the  body are these particles going, how long do they stay there, and what are they doing while they’re there? Another concern is this idea of accumulation of these particles in healthy human tissues. A study out of Hawaii has shown that tissues sampled [recently] had significantly higher concentrations of plastic particles in them than the tissues from just 10 years ago. So while it might not affect my health today, it may affect my health in 50 years.

What was so unique about this study?

Stapleton: Because we were able to find these nanoplastics. That was important because as scientists we knew that they were there [in bottled water], but we hadn't been able to demonstrate that, show them, count them and identify what type of plastic they were made from.

 Are you still drinking bottled water?

Stapleton: I’m drinking filtered tap water now [tap water generally contains less plastic particles than bottled water], but I’m still nervous about the filters because they’re made out of plastic and they can’t filter out nanoparticles.

PLASTIC BE GONE!

Here are some additional tips from Aidan Charron, Earthday.org ’s director of End Plastics Initiatives, on how to begin purging plastics from your home and life.

Reuse! Ditch the single-use plastic and opt for stainless steel or glass water bottles and food containers.

Eco-Friendly Fashion Pay attention to what your clothes are made of. Avoid synthetic fibers — they’re plastic.

Audit Your Plastic Use Find more sustaibable alternatives like shampoo bars for daily needs.

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