time to roll down the ramp mass of the ball diameter of the ball kind of surface on the ramp
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Students design an investigation to study the effect of different surfaces on the speed of a ball rolling down a ramp. Which of these is the independent variable?
Possibilities:
- time to roll down the ramp
- mass of the ball
- diameter of the ball
- kind of surface on the ramp

kind of surface on the ramp