In a scientific experiment, the variable manipulated or controlled by the experimenter is called the

The variable manipulated or controlled by the experimenter is called the independent variable.

Example:

If the flow velocity at the bottom of a tank is measured by varying the height of water in the tank, we are measuring velocity as a function of water height.

Therefore,

water height = independent variable (controlled)

velocity = dependent variable (measured in response to water height).

Mathematically,

v = f (h)

where v = response variable (dependent)

h = controlled variable (independent).