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How do I define variables? If
you increase the temperature of an oven, cake will bake faster. In other
words the TIME it takes for the cake to bake DEPENDS on the TEMPERATURE
of the oven. If your project
title is "How does the oven temperature affect the baking time of a
cake?", one thing that you need to do is identifying the variables. In
this example BAKING TIME and OVEN TEMPERATURE are the two variables that
we measure, record and use them to draw a conclusion. Temperature
of oven is what you set. For example you may set temperature to 350ºF
and bake a cake. Temperature is what you manipulate and is not depended
on any other factor. That is why you call temperature an independent
variable. It is also called manipulated variable. We call it manipulated
variable because you manipulate or change it in order to see how does it
affect the baking time. On the
other hand, the BAKING TIME depends on the temperature. That is why you
call it DEPENDENT variable. Changes in the BAKING TIME is in response to
the TEMPERATURE. So you can also call it RESPONDING variable. While
you are doing your experiments, some other changes may happen in the
environment that make your results unreliable. For example you may test
baking a cake in the morning at 350ºF and another cake in the afternoon
at 400ºF. You may bake one of them in a small oven and the other one in
a big oven. You may bake one cake in the lower shelf of the oven and the
other one in the upper shelf of the oven. Such
variations will make your results unreliable. For example if your
conclusion shows that "cake will bake faster at higher
temperatures", someone may challenge your results and argue that
"One of the cakes baked faster because it was in a smaller oven, or
because it was at the lower shelf or because it was baked in the
afternoon". How do you know that the temperature was the only
factor affecting the baking time? To
avoid such arguments, you also define some controlled variables and some
constants. For
example you may use two identical ovens and cook both cakes at the same
time and use the upper shelves of the ovens.
Independent variable (also known
as manipulated variable) is a condition or factor that we change or
choose in order to see how it affects other variables. Dependent
variables (also known as responding variables) are conditions that
are affected by any change in the independent variable. Controlled
variables are variables such as room temperature, light and other
environmental factors that you cannot keep constant; however, you can
make sure that all experimental runs are performed under the same
conditions. Constants are
values such as the size of oven, the size of pan, the ingredients of the
cake, the size of the cooking pan, the amount of material.
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