# Video: Uncontrolled Variables in Experiments

Which of the following statements most correctly defines an uncontrolled experimental variable? [A] An uncontrolled experimental variable is a quantity that cannot change in value. [B] An uncontrolled experimental variable is a quantity that does not change in value during an experiment. [C] An uncontrolled experimental variable is a quantity that predictably changes in value during an experiment. [D] An uncontrolled experimental variable is a quantity that may unpredictably change in value during an experiment.

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### Video Transcript

Which of the following statements most correctly defines an uncontrolled experimental variable? A) An uncontrolled experimental variable is a quantity that cannot change in value. B) An uncontrolled experimental variable is a quantity that does not change in value during an experiment. C) An uncontrolled experimental variable is a quantity that predictably changes in value during an experiment. D) An uncontrolled experimental variable is a quantity that may unpredictably change in value during an experiment.

Alright, so, we have these four answer options, and we wanna pick which one most correctly defines this term uncontrolled experimental variable. To see which of these options is the best match, let’s think of an example of an uncontrolled experimental variable. In general, an experiment is conducted for the purpose of testing out a prediction that we have. A prediction can be just about anything. Let’s say that our prediction is that if we drop a ball to the ground, then the higher the ball is when we release it, the faster it will be travelling when it lands. So, that’s our prediction. And we can design an experiment to test it out.

In this experiment, there are different kinds of variables. One is called the independent experimental variable. And that’s the factor, or the variable, that we deliberately change. In this case, that would be the height of the ball above ground when it’s released. Related to that is a variable called the dependent variable. In this case, that would be the speed of the ball when it lands. But even beyond independent and dependent variables, there are other types involved. For example, the weather conditions on the day that we conduct our experiment.

Let’s say that it happened to be a very windy day. We can see how that might affect our results. Depending on its direction and speed, which we can’t control, the wind could either slow down or speed up the falling ball. So, the wind is an uncontrolled experimental variable in this case. It may change in value over the course of our experiment. And we can’t control how it does or if it does.

So, if that’s an example of an uncontrolled experimental variable, let’s reevaluate our four answer options and see which one describes something like that. Option A tells us that an uncontrolled experimental variable is a quantity that cannot change in value. As we’ve seen though, an uncontrolled experimental variable is indeed a variable, something that can change in value. Option A is talking about a fixed value, a universal constant. So, we’ll cross that off our list.

Option B says, an uncontrolled experimental variable is a quantity that does not change in value during an experiment. But considering again our example experiment of the dropped ball and the wind speed, we see that, in fact, an uncontrolled experimental variable may well change in value during an experiment. And moreover, that’s not something we’re able to control. That’s the uncontrolled nature of this variable. So, option B is not our answer either.

Option C says that an uncontrolled experimental variable is a quantity that predictably changes in value during an experiment. Well, this actually sounds more like an independent experimental variable, the variable that we deliberately and purposefully change. When the changes are predictable, as this answer option says, then the variable is not uncontrolled. It’s one that we can control. We won’t choose option C either.

That leaves us with option D, an uncontrolled experimental variable is a quantity that may unpredictably change in value during an experiment. And that’s a very good description of the wind in our dropped ball experiment. The wind could stay constant, or it could die down to zero, or it could vary. We can’t predict how it will behave. This is a perfect description of an uncontrolled experimental variable, so we choose this as our answer. An uncontrolled experimental variable is a quantity that may unpredictably change in value during an experiment.