What is a control in a science project?

help me!!! plz explain in simple wordsWhat is a control in a science project?
Say you want to test a cure for headaches. You get a few people with headaches, give them medicine. After an hour, most of them get better. Did the cure work ? Well, maybe. Or maybe the headaches just went away on their own.





The solution is that instead of giving the medicine to everyone, you give it to half the group. The other group, which gets no medicine, is the ';control group'; : it tells you what happens in the absence of treatment. If you see a difference between the control group and the group who actually got medicine, then you really know that the medicine did work.





(Actually in such experiments the control group is usually given a ';placebo';, something that looks exactly like the real medicine but has no active ingredients. This accounts for the fact that the mere act of giving someone ';medicine'; -- or something similar looking -- usually makes that person feel better...)What is a control in a science project?
A control is an additional experiment you run alongside your real experiment. It is identical in every way to your test experiment, except for the one thing you are testing. For example, say you want to know if putting an aspirin in the soil will make flowers more colorful. So you grow a group of plants, put an aspirin in the soil, and the plants produce very colorful flowers. What have you demonstrated? Nothing! Because there are dozens of reason why plants might produce very colorful flowers - materials already in the soil, temperature, light, humidity, etc. What you should have done is to grow two identical sets of plants, same seeds, same pots, same soil, same water, same light, same humidity, etc. In one set you put an aspirin in the soil. In the other set - the control set - you don't. Now, if the set with the aspirin have more colorful flowers than the set without the aspirin, you have demonstrated something real because the control rules out all other possible explanations for the flower color.
Ussually refers to a ';control or control group'; meaning something unchanged or unexposed to the experiment to be used as a reference to measure change or an effect