Baz and Jae
The Physics of Spikeball
Intro
When a ball bounces against a surface, a Newton's third law interaction causes both the surface and the ball to enact a force on the other. This exchange happens quickly, reversing the momentum of the ball and causing it to “bounce”. This quick interaction resulting in a change in momentum is called a collision, and the force enacted on the ball is called an impulsive force. The Impulse (I) of an interaction is defined as the area under the force versus time curve, and is equal to the change in momentum of the object. In our DYO, we aimed to investigate how balls of various compositions would bounce on a Spikeball net by measuring the rebound height at three different drop heights. Our goal was to find what type of ball performed the best (bounce highest), as well as what physical properties contribute to this success.
https://byjus.com/physics/impulse-units/
Background
As mentioned in the introduction, collisions cause a rapid change in momentum due to Newton’s third law interactions between an object and a surface. Against a rigid surface, a ball will deform as it pushes against the surface (compression), before springing back to its original shape as it is pushed away from the surface (expansion). In our case, however, our surface is non-rigid, and instead the majority of deformation is in our surface (the spikeball net) as opposed to the objects (the balls). Although the same concepts of impulse apply, our non-rigid surface may have an effect on ball-bouncing, especially because ball weight as opposed to composition will be the main cause for deformation.
https://interestingengineering.com/what-are-the-physics-behind-bouncing-balls
Methods
For our experiment, we selected 6 balls of various weights, volumes, and compositions to test the effects of these characteristics on rebound. The balls we selected were a lacrosse ball, a foam ball, a basketball, two tennis balls (one weighted and one unweighted) and a regular Spikeball. We dropped the balls at three different heights (65, 115, and 165 centimeters) and recorded video using our phones. We had a measuring stick in the frame of the video so we could determine how high the ball bounced up.
Results
We found that the heavier balls performed worse (bounced lower) than the lighter ones. The weighted tennis ball, the heaviest ball we tested, bounced the lowest at every drop height. The unweighted tennis ball, which was the second lightest ball tested, performed the best at every drop height, suggesting that this discrepancy can be attributed to weight alone and not composition. Interestingly, we found that the lacrosse ball outperformed the Spikeball at each drop height despite having twice the mass, possibly suggesting that more rigid compositions (such as tennis ball and lacrosse ball) bounce higher against the net than less rigid ones (foam ball and Spikeball).
Discussion
Our results suggest that ball weight is negatively correlated with rebound height against a net. The heaviest objects (basketball and weighted tennis ball) performed consistently worse than the lighter objects, and the unweighted tennis ball performed the best overall, suggesting that the change in mass causes lower bounces against the net. This is likely because the heavier balls cause more deformation of the net, dispersing energy out of the system. Also, the foam ball and Spikeball performed worse than expected based on their weights, suggesting that their squishier composition contributed to a lower bounce height due to energy loss from deformation.