What is a control and variable in a science experiment?

I am doing a science experiment where I am testing how effective different soap brands are at removing permanent marker on skin as well as the frothiness. I am using five soap brands to test this and one permanent marker. What are the control and variables?|||a control is something that does not change. a variable is something that does change. so in your case the control might be how much soap you use on each stain, how big the stain is, the time spent trying to remove stain. your variable will be your soaps because you are changing the brands.|||The variable in an experiment is that aspect of the experiment that you change in order to bring about the effects you hope to see - in your case, the brand of soap. You have to make sure that everything else in the experiment remains constant - the time of washing, the temperature of the water, the amount of soap used, etc. Otherwise you will have multiple variables, and it will be impossible to tell whether the observed effects are due to your intended variable or not. For example, if you use 1 gram of soap A and 5 grams of soap B, and Soap B does a better job, you can't say that Soap B really works better, because the difference might be due only to the different amounts used. Or, if you use 1 gram of Soap A with water at 70 degrees, and 1 gram of Soap B with water at 90 degrees, again, you cannot say that any observed difference is due to the different soaps, because you have introduced another variable - temperature.





A control is an additional experiment you run alongside your test experiments, to make sure that what you are testing is the real cause of what you are seeing. In other words, the control is exactly the same as the test experiments, except you don't use the test variable in the control experiment. In your case, someone might say "It is probably just the warm water that is removing the ink, and the soap has nothing to do with it". OK, they have a point. That could be true. You can prove that isn't so by running a control - you wash with the same water, at the same temperature, for the same length of time, but you don't use ANY of the soaps! That experiment is your control, and you can compare the results of your other experiments, the ones with the soaps, to the results of the control experiment, to show that it really is the soap that is making the difference.