|MadSci Network: Environment|
Hello, Tiffany. When I was in school, I also sometimes had trouble understanding what the different scientific words were supposed to mean. In science, we try to give words very precise meanings - and when we do, we often make even simple things sound so complex that they get really, really confusing. Oh, well. Let me see if I can help make things a bit clearer for you. When you run an experiment, you change some things, and see what happens. That is what your teacher meant when he said something like "manipulative variables mean change". The word "manipulate" means to control something. So, a manipulative variable is a variable that you control by changing it. For example, if your experiment is to make pancakes and see how good they taste, you might change how much milk you add in the recipe - so, the amount of milk would be your manipulative variable. You might compare one batch of pancakes where you followed the recipe on the pancake box exactly: 1 cup of pancake mix, 1 cup of milk, 1 egg, cook at medium..... .....and another batch where you just changed the amount of milk: 1 cup of pancake mix, 2 cups of milk, 1 egg, cook at medium. Now - here is the confusing part, and probably the reason your teacher said that "manipulative variables mean change", rather than "manipulative variables are the ones you control" ....ready?...Okay...here comes the confusing part... After you changed the amount of milk in your pancake experiment, you compared the pancakes where you changed the amount of milk, to the pancakes you make where you don't change the amount of milk..... and we often call the pancakes we didn't change anything on (made following the recipe on the box) ...."the CONTROL group"! So, your teacher didn't want to call the manipulative variable "something you control" because...well, that might confuse you later when you learn about control groups where nothing is changed. Yep, we sometimes make things very confusing. Also...well, there are many variables you could have changed in your pancake experiment. You could have changed how much pancake mix you added, or how many eggs you added, or what temperature you cooked at. All of these are controlling variables that you could have changed. But, you decided to only change the amount of milk - so milk is the only manipulative variable, the only variable you changed in your experiment. Now, suppose you had decided instead to have several different batters you tried in your pancake experiment - one control group where you followed the recipe: 1 cup of pancake mix, 1 cup of milk, 1 egg, cook at medium..... ...and a second set of pancakes where you changed how many eggs: 1 cup of pancake mix, 1 cup of milk, 2 eggs, cook at medium..... .... and a third set of pancakes where you changed the heat: 1 cup of pancake mix, 1 cup of milk, 1 egg, cook at low ..... Now, you have two manipulative variables: eggs and heat. You left the amount of milk and the amount of pancake mix constant, rather than manipulating them. I hope that makes sense. If you need further help, here's a webpage that explains this further: Complex Science Processes: Definitions and Indicators Responding variables are what you look at to see the results of what you manipulated. In the pancake example, your responding variable might be how high the pancakes rise. Maybe the pancakes that you made with 2 cups of milk are really flat while the control group pancakes are nice and fluffy - that fluffiness is the result, the responding variable. Or, maybe you had 3 friends taste one pancake from each group and give a rating from 0 to 10 on how good it tasted, and you added up their ratings. Following the recipe on the box, the pancakes in the control group got rated a 7 by Jeannie, an 8 by Paul, and a 10 by Freddie who loves pancakes. Adding these up, the control group got a taste score of 7 + 8 + 10 = 25. In the group where you manipulated the amount of milk and used twice as much milk, the pancakes got rated a 5 by Jeannie, a 2 by Paul, and a 10 by Freddie who loves pancakes no matter how flat or runny they are. So, while the control group got a taste score of 25, and the pancakes with two cups of milk used got a taste score of 17. The taste score is the responding variable - it is the result that is affected by the variable you manipulated.
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