i have to do a science project for science i have to compare to products and only one variable can change?

Question

scientific method
data
graph

Answer 1

For my daughter's science class we compared brands of tennis balls for 'bounce'. We dropped the balls from a fixed height onto a board set at 45 degrees and then into some sand. We measured the distance from the edge of the board to the mark in the sand left by the ball. Experiment was cheap and our dogs enjoyed the balls after we were done. One recommendation, we only dropped the balls from 4 feet and got only got small differences between the brands. I suggest dropping them from a higher distance, 8 or 10 feet, it should increase the effect you sees.

You could also test how long they maintain their bounce. Measure the bounce 'out of the can' and then play tennis with the ball for a fixed period of time, and repeat the bounce experiment.