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The Scientific Method

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The Steps of the Scientific Method for Kids - Science for Children: FreeSchool

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DCSD Science & Engineering Fair Overview

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Need help finding a project idea?

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Browse Science Projects

Over 1,200 free science projects for K-12. Browse by subject, grade level, or try our Topic Selection Wizard to find your winning science project. With science projects in 32 different areas of science from astronomy to zoology, we've got something for everyone!

Let us help you find a science project that fits your interests, with our Topic Selection Wizard.

15 Best Science Projects - Our Scientists' Picks

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Over 1,200 free science projects for K-12. Browse by subject, grade level, or try our Topic Selection Wizard to find your winning science project. With science projects in 32 different areas of science from astronomy to zoology, we've got something for everyone!

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Understanding Variables

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What are Variables?

What are Variables?

In science, a variable is any factor, trait, or condition that can exist in differing amounts or types.

Scientists try to figure out how the natural world works.To do this they use experiments to search for cause and effect relationships. Cause and effect relationships explain why things happen and allow you to reliably predict the outcomes of an action. Scientists use the scientific method to design an experiment so that they can observe or measure if changes to one thing cause something else to vary in a repeatable way.

These factors that change in a scientific experiment are variables.

A properly designed experiment usually has three kinds of variables: independent, dependent, and controlled.

What is an Independent Variable?

The independent variable is the one that is changed by the scientist. Why just one? Well, if you changed more than one variable it would be hard to figure out which change is causing what you observe. For example, what if our scientific question was: "How does the size of a dog affect how much food it eats?"; then, during your feeding experiments you changed both the size of the dog and the time of day the dogs were fed. The data might get a bit confusing- did the larger dog eat less food than the smaller dog because of his size or because it was the middle of the day and dogs prefer to eat more in the morning?

Sometimes it is impossible to just change one variable, and in those cases, scientists rely on more-complicated mathematical analysis and additional experiments to try to figure out what is going on. Older students are invited to read more about that in our Experimental Design for Advanced Science Projects page. To be clear though, for a science fair, it is usually wise to have only one independent variable at a time. If you are new to doing science projects and want to know the effect of changing multiple variables, do multiple tests where you focus on one independent variable at a time.

What is a Dependent Variable?

The dependent variables are the things that the scientist focuses his or her observations on to see how they respond to the change made to the independent variable. In our dog example, the dependent variable is how much the dogs eat. This is what we are observing and measuring. It is called the "dependent" variable because we are trying to figure out whether its value depends on the value of the independent variable. If there is a direct link between the two types of variables (independent and dependent) then you may be uncovering a cause and effect relationship. The number of dependent variables in an experiment varies, but there can be more than one.

What is a Control Variable?

Experiments also have controlled variables. Controlled variables are quantities that a scientist wants to remain constant, and she or he must observe them as carefully as the dependent variables. For example, in the dog experiment example, you would need to control how hungry the dogs are at the start of the experiment, the type of food you are feeding them, and whether the food was a type that they liked. Why? If you did not, then other explanations could be given for differences you observe in how much they eat. For instance, maybe the little dog eats more because it is hungrier that day, maybe the big dog does not like the dog food offered, or maybe all dogs will eat more wet dog food than dry dog food. So, you should keep all the other variables the same (you control them) so that you can see only the effect of the one variable (the independent variable) that you are trying to test. Similar to our example, most experiments have more than one controlled variable. Some people refer to controlled variables as "constant variables."

In the best experiments, the scientist must be able to measure the values for each variable. Weight or mass is an example of a variable that is very easy to measure. However, imagine trying to do an experiment where one of the variables is love. There is no such thing as a "love-meter." You might have a belief that someone is in love, but you cannot really be sure, and you would probably have friends that do not agree with you. So, love is not measurable in a scientific sense; therefore, it would be a poor variable to use in an experiment.

Examples

Examples of Variables

Time as an Example of an Independent Variable

In some experiments, time is what causes the dependent variable to change. The scientist simply starts the process, then observes and records data at regular intervals.

The Independent Variable for Surveys and Tests of Different Groups

When a scientist performs a test or survey on different groups of people or things, those groups define the independent variable. For example:

Either/Or (Binary) Variables

Sometimes a variable simply represents an either/or (binary) condition. For example, something might be either present or not present during an experiment.

Sample

Sample

Here is a sample containing the variables and hypothesis.

Checklist

Science Fair Project Variables Checklist

Assign these with Google Classroom:

Explore Our Science Videos

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How to use dependent, independent, and controlled variables in your science experiments.

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The Engineering Design Process

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The Engineering Process: Crash Course Kids #12.2

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(4th & 5th Grade)

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When designers present their work, they don't just put it in front of the client and wait for a reaction; they provide a rationale that explains how the design solution answers the brief. The rationale can take different forms, from a simple verbal explanation to an interactive on-screen presentation that leads the client through the thinking and the development process to the solution.

A well-written design rationale can be invaluable in explaining how your design solution satisfies the brief. Choices that you have made, even those not immediately obvious to the client, can be explained, helping to show the clarity of your thinking, the benefits of your solution, and ultimately to help sell your idea.

For students, written rationales are often required as project deliverables, but they can also be useful for organizing your thoughts before classroom presentations or putting together case histories of projects for print or online portfolios. When writing your rationale it's always helpful to have access to some visual documentation of your design process - from your initial sketches onwards - especially for case histories. Keep those sketchbooks!

Some things to keep in mind when writing your rationale are:

1. At the top of the page, at the very minimum state the name of the client and the name of the project. It's sometimes also helpful to provide a short summary of the brief.

2. Keep your writing to the point - one page is usually long enough.

3. Start by explaining the overall concept of your design - what is it, who is it for (audience) and in what context will it be used? Then go into details, giving reasons for the design decisions that you've made.

4. Remember - it's a rationale (requiring the reasons or logic behind your decisions), not a description. Don't just say what you've done - explain why you've done it, referring back to the creative brief, the audience, your research, and the information that is to be communicated.

5. Don't admit to arbitrary decision-making or say that you used a particular colour/font/technique just because you like it. Every choice you've made should be relevant to the brief. What effect does the colour/font/technique have? What does it communicate? If it's not relevant, don't mention it.

6. Keep your reasoning honest. It's easy to spot convoluted after-the-fact rationalizations that sometimes stretch believability.

7. Don't focus on your process or on approaches you rejected unless they provide an explanation for the final work - and don't mention what you would have done if you'd had two more weeks to work on it. It's time to present your work, and you should do so with as much confidence as possible.

8. Don't pass judgment on your own work, whether positive or negative. It's necessary to say why and how it satisfies the brief, but nobody wants to read: "this solution is amazing" (we'll make up our own minds, thanks) or: "this isn't my best work" (this will not get you far in the real world).

9. Aim for clarity and readability in the design and typography. Use headings (and sub-headings if necessary) and split your writing into paragraphs. Don't over-design the page!

10. This should go without saying, but use good grammar and spell check before you print. It can be helpful to enable dynamic spelling in InDesign (InDesign > Preferences > Spelling). And don't forget the "e" on the end of the word "rationale"!

A useful guide for writing the rationales for submissions to the GDC National Scholarships!

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Writing a Project Rationale: A guide for students

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When designers present their work, they don't just put it in front of the client and wait for a reaction; they provide a rationale that explains how the design solution answers the brief. The rationale can take different forms, from a simple verbal explanation to an interactive on-screen presentation that leads the client through the thinking and the development process to the solution.

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Fillable Forms (Form 1, 1A, 1B, and 3 ONLY)

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Fillable Forms (Form 1, 1A, 1B, and 3 ONLY)