Physics

10.1 - Variables & Controls

2 min

note 1 of 2

The three kinds of variable

Every experiment has one variable you change, one you measure, and several you keep the same.

Variable	What it is	Example: insulation and cooling
Independent	The one thing you change on purpose	The number of layers of insulation
Dependent	The thing you measure to see the effect	The temperature drop in ten minutes
Control	The things you keep the same	Volume of water, starting temperature, the same beaker and lid

Spotting which is which

Read the aim as "how does X affect Y": X is the independent variable and Y is the dependent variable.
On a graph, the independent variable goes along the x-axis (bottom) and the dependent variable goes along the y-axis (side).

note 2 of 2

Controls and valid results

Control variables are the factors you keep the same, such as the volume of water and the temperature it starts at.
Keeping them constant is what makes the results valid: if only the independent variable changes, any change in the result must be down to that variable and nothing else.
When you name a control variable, name it in full: "the volume of water", not "the conditions".

Control experiment

A control experiment is a separate set-up with the factor you're testing left out, run for comparison.
For example, to show that insulation slows cooling, set up an identical beaker with no insulation at all. Comparing the two cooling rates shows the difference the insulation made.

key terms

TermDefinition

Independent variableThe variable that you choose to change in an experiment.

Dependent variableThe variable that you measure to see the effect of changing the independent variable.

Control variableA variable that is kept the same throughout an investigation so that only the independent variable can affect the results.

ValidDescribes a result from a fair test, where all other variables were controlled so that any effect is due to the variable being changed.

Control experimentA copy of the experiment without the factor being tested, set up alongside it to show that any effect is caused by that factor.

end of notes

Key points to remember

The three kinds of variable

Every experiment has one variable you change, one you measure, and several you keep the same.

Variable	What it is	Example: insulation and cooling
Independent	The one thing you change on purpose	The number of layers of insulation
Dependent	The thing you measure to see the effect	The temperature drop in ten minutes
Control	The things you keep the same	Volume of water, starting temperature, the same beaker and lid

Spotting which is which

Read the aim as "how does X affect Y": X is the independent variable and Y is the dependent variable.

On a graph, the independent variable goes along the x-axis (bottom) and the dependent variable goes along the y-axis (side).

Controls and valid results

Control variables are the factors you keep the same, such as the volume of water and the temperature it starts at.

Keeping them constant is what makes the results valid: if only the independent variable changes, any change in the result must be down to that variable and nothing else.

When you name a control variable, name it in full: "the volume of water", not "the conditions".

Control experiment

A control experiment is a separate set-up with the factor you're testing left out, run for comparison.

For example, to show that insulation slows cooling, set up an identical beaker with no insulation at all. Comparing the two cooling rates shows the difference the insulation made.