Controls or controlled variables are variables that should remain unchanged in the experiment. These variables can have a direct effect on the dependent variable. Take note that controlled variables are NOT what is being tested but can alter results. Three possible controls for this experiment would mainly be features of the ball and the ramp.
Examples and possible answers to your question would be:
1. Mass of the ball
2. Size of the ball
3. The density of the ball
4. Type of ball
5. Length of the ramp
6. Type of ramp
7. The thickness of the ramp
Other controls that you can consider also is the environment. Wind can also affect the ball that is being rolled.
