Variables & Controls in a Science Experiment

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  • 0:01 Science Experiments
  • 1:08 Variables and Controls
  • 3:19 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After watching this video, you will be able to explain how science experiments are conducted; what variables, controlled variables, and controls are: and why these things are important. A short quiz will follow.

Science Experiments

A science experiment is a way of figuring out the structure and behavior of the world using a systematic method. In a science experiment, we're usually trying to find out the relationship between two things: For example, how does being sleepy affect the number of car crashes? Or how does putting carbon dioxide in the atmosphere affect the temperature? We want to know if two things affect each other and how they affect each other if they do.

The scientific method is a way of conducting investigations to make accurate conclusions using systematic observation, measurements, experiment, and modification of hypotheses. You conduct an experiment using a strict, reliable method; take measurements carefully and repeatedly; analyze that data in a logical way; and make conclusions from it. This is what science is all about. It's a process by which we come up with an accurate picture of how things in the universe affect each other.

But how does science make sure our data can be relied upon? Humans are really good at making mistakes. This is where variables and controls come in.

Variables and Controls

A variable is a number or feature that is changeable - that can have lots of different possible values. A variable is a thing you might measure in an experiment, like the length of a block of wood, or the time an object takes to fall, or how thick the leaves of a plant are, or on a scale of one to ten how angry a human being says they are.

If you want to really know how two factors affect each other, your experiment must focus on just two variables. For example, you might want to find out how different amounts of light affect the growth of a plant. You can change the amount of light by putting different plants in a dark closet for different amounts of time.

But plants don't just need light to grow. They also need air and water. Those are variables too. In order to get accurate data from such an experiment, we would need to make sure that those other variables are not affecting the result. For example, we would want to make sure that we watered the plants in exactly the same way and with exactly the same amount of water. If we didn't, we wouldn't know whether the growth of a plant was because of the light or because of the amount of water.

The amount of water in this experiment is an example of a controlled variable. A controlled variable is something that is kept the same in an experiment. In a scientific investigation, one variable is changed (like the amount of light) and one resulting variable is investigated (the amount of growth), and ideally everything else is kept exactly the same.

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