Change keeps the mixing time a constant.Likewise if

Change is usually considered a good thing.

However, in a science experiment, it’s really important to not change some things. In this lesson, learn why constants are so critical to sound experimentation.

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Constants Are Critical

Mercedes wants to make cookies, but she’s not sure which temperature will produce the best-tasting cookies so she decides to experiment. She will cook one batch of cookies at 325 degrees, one at 350 degrees, and one at 375 degrees. Which will be tastiest?In an experiment, the goal is to answer a specific question. To answer that question, you make one specific change, observe the effects, record the data, and draw your conclusion.

The one thing that is changed in the experiment is known as the manipulated variable. The effect this change produces is measured and is known as the responding variable.To understand the relationship between the manipulated variable and responding variable, it’s important for the scientist to keep everything else identical. Why? Because this allows the scientist to know if the one change is causing the effect.

Let’s get back to the experiment. Remember, Mercedes wanted to know which cooking temperature makes the most delicious cookies, so she only changed the oven’s temperature. Everything else in the experiment stayed the same.If a scientist conducted an experiment, but changed everything at once, he’d have no idea which change produced the result. For example, if Mercedes changed the oven’s temperature, the recipe, the baking sheets, and the cooking time, how would she know which change affected the cookies’ outcome?! She could never know because she changed too many things at once. For this reason, a constant, or an unchanging variable, is critical in a science experiment.

An Experiment with Constants

Now, Mercedes is performing an experiment with bubbles. Specifically, she wants to know what bubble mix makes the longest lasting bubble. She makes three bubble mixes using different ingredients. They’re in identical jars, so she labels them #1, #2, and #3.Next she stirs bubble mix #1 for 30 seconds, dips a bubble wand into it and blows a bubble. Using a stopwatch, she measures how long it takes the bubble to pop. She repeats it with bubble mixes #2 and #3, stirring each for 30 seconds and using an identical bubble wand and stopwatch.

What in Mercedes’s experiment is staying constant, or in other words, what is not being changed? Each bubble mix had different ingredients, so these are not constants. But Mercedes kept the jars, the mixing time, the bubble wand, and the stopwatch the same, so these are the constants.Mercedes is smart. She knows that if she mixed one bubble solution for ten seconds, and another for 100 seconds, the results might be altered. She’s curious about the bubble ingredients that make the longest-lasting bubble, so she keeps the mixing time a constant.Likewise if Mercedes used a small bubble wand for mix #1 and a large bubble wand for mix #2, this may have skewed her results. She’s not trying to see what size bubble wand produces the longest-lasting bubble, so she keeps the bubble wand identical.

Lastly, let’s establish Mercedes’s manipulated variable. The thing she changed was the ingredients in the bubble mixes, so this was her manipulated variable. Her responding variable, or the thing that altered because of her changes, was the length of time it took the bubble to pop.

Lesson Summary

The manipulated variable is the one thing the scientist changes in the experiment. The responding variable is the measurement that shows the effects this specific change caused. Everything else in the experiment should be a constant, or an unchanging variable throughout the experiment.


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