In Science, what are dependent and independent variables?

Question

And also, what's a rationale?
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Answer 1

The other answers have the dependent and independent variables covered, so here's some info on the rationale. The rationale is the most important part of the experiment. It is the explanation why the experiment turned out as it did. Another way of looking at it is the rationale is the way in which the independent variables caused the response in the dependent variable. For example if you were testing the hypothesis that a potted plant will grow faster at 80 degrees compared to a plant at 70 degrees, temperature is the independent variable and growth is the dependent variable.

Let's say that the plant grown at the higher temperature ended up growing just a little more than the other plant, but not a very big difference. The rationale is your thoughts explaining why a small difference in growth occurred, and maybe why a large difference did not occur. You might reason that the temperature difference is not large enough, or maybe you might conclude that plant growth is affected more by the amount of fertilizer and water, because the effects of water and fertilizer are well-established as mechanisms affecting plant growth.

If a big difference growth occurred, you would want to explain why temperature has such a large effect, which might be explained by higher rates of transpiration and chemical reactions that occur at higher temperatures. Maybe another reason is that the plant grows naturally in an environment that is very hot, so it stands to reason that the highest growth rate occurs near temperatures where the plant occurs naturally.

Usually when providing rationale, you cite other types of science findings such as chemistry needed to explain rates of chemical reactions, and maybe some other information on plant biology related to growth.

Answer 2

Okay, the independent variable is the "thing" that you manipulate to find how the dependent variable reacts to it (think of it as the X-axis of a graph). The dependent variable changes as the independent variable changes. For example: if you're heating a glass of water and measuring the volume of the liquid over a length of time, the temperature would be the independent variable and the volume would be the dependent variable because it is changed as the independent variable (the temperature) is increased or decreased. Sorry if this confused you. You can always think of the dependent variable as the Y-axis of a graph and the independent variable the X-axis, hope this helps.

Answer 3

Independent Variable - the factor you manipulate in an experiment.

Dependent Variable - the factor that is changed (or the factor that depends) with the independent variable.

Answer 4

Independent variable - Variable you are manipulating
Dependent variable - what is being measured