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| Hypothesis: Trees sprout leaves in the spring when they get at least 12 hours of daylight | ||||||
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| Many things , or factors, might make one tree sprout leave sooner or later than another tree. The amount of water that the trees receive might make a difference. Changes in temperature might make a difference, too. These factors are called variables. A variable is any factor that can change in an experiment. | ||||||
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Imagine that in your experiment, you give your trees different amounts of water and you expose them to different amounts of light and you keep them at different temperatures.
Suppose that Tree A sprouted leaves before Tree B. How can you tell which variable made Tree A sprout leaves first? You can't tell because you don't know which variable caused the earlier sprouting. |
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| In every experiment, you have to keep all the variables the same except the one you are testing.
In this experiment, all the variables except light are controlled. Both trees get the same amount of water. Both trees are kept at the same temperature. Only the amount of light hitting the trees is different. What caused Tree A to sprout leaves earlier than Tree B? More light! |
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