Suppose you are trying to determine whether the weight of the ball, the height or length of the ramp will affect the amount of time it'll take for a ball to roll down a ramp.
If possible, an alternative is to borrow something like this from the science department:
Goal: To identify which of the three variables affects the amount of time
Create a two-way table to organize your data. An example of a possible two-way table is:
You would duplicate this two-way table two more times to take into account the three different heights.
The times you enter in the table on the left will be the results of the experiment where the height of the ramp remained constant.
Based on your experiment: