Holy balls!

TL;DR

This paper investigates why a Waboba ball skips better on water than other balls, attributing it to its elastic deformation and ability to plane on the water surface, similar to a skipping stone.

Contribution

It reveals the role of elastic deformation and shape change in water skipping behavior, providing insights into the physics of bouncing balls and stones.

Findings

Waboba can skip over water more than 20 times and travel nearly 60 meters.

Elastic deformation allows the Waboba to flatten and plane on water, enhancing skipping.

Different balls' rebound behaviors are explained by their elasticity and impact angles.

Abstract

We demonstrate the behavior of three balls skipping off of the water surface: a Superball, a racquetball, and a water bouncing ball (Waboba). The three balls have rebound coefficients of 0.9, 0.8 and 0.2, respectively. However, we notice that the Waboba bounces better than the others, but why? The Superball has a high coefficient of restitution, creating large rebounds. Here the impact is angled to the free surface, but the inelastic response and large mass ratio forces the ball underwater without skipping. The racquetball has a lower mass ratio and a more elastic response to impacts. Also thrown at a shallow angle, it bounces off of the surface of the water 1-3 times before coming to rest. The Waboba flattens inside the cavity allowing it to skip off of the surface more easily. The flattened ball looks more like a skipping stone than a sphere due to its large elastic deformation at impact. Examining the reaction of a skipping stone we see that the stone creates a cavity in which it planes, slipping out of it with some upward velocity. The Waboba behaves like a skipping stone planing on the surface of the water, allowing it to bounce upwards of 20 times and traveling nearly 60 meters. While some skill is needed to throw the Waboba across a pond, It adapts to each skip because of its elastic response, whereas the stone must be thrown perfectly in order to gain the best skipping advantage.