As the scientist changes the independent variable, he or she observes what happens.
The scientist focuses his or her observations on one dependent
variable to see how it responds to the change made to the independent variable.
The new value of the dependent variable is caused by and
depends on the value of the independent variable.
For example, if you open a faucet, the independent variable,
the quantity of water flowing, dependent variable changes in response.
You observe that the water flow increases.
The number of dependent variables in an experiment varies, but
there is often more than one.
Experiments often have controlled variables.
Controlled variables are quantities that scientists wants to remain constant and
he or she must observe them, as carefully as the dependent variables.
For example, if you want to measure how much of water increases when you
open a faucet, it is important to make sure that the water pressure,
the control variable is held constant.
That's because both the water pressure and
the opening of a faucet have an impact on how much water flows.
If we change both of them at the same time, we can't be sure
how much of the change in water flow is because of the faucet opening and
how much, because of the water pressure.
In other words, it would not be a fair test.
Most experiments have more than one controlled variable.