# Why the rubber ball bounced higher than the glass ball?

For a teaching degree we did the following experiment:

Drop a rubber and a glass ball of approx. same size from approx. same height onto laminate flooring.

As we expected, the rubber ball bounced higher than the glass ball.

Our explanation: The rubber ball is more efficient in converting the kinetic energy into deformation energy and back. So the rubber ball transforms less energy into heat.

But alas, attempted verification with a heat camera showed otherwise: While there was a big blotch of heat left behind on the table by the rubber ball, the mark by the glass ball was barely visible.

The lecturer was very vague and eluded our question for an explanation.

So my question is:

What is the correct explanation of this? And why does the glass ball not produce at least an equal amount of heat?

Before posting here I googled this problem and to my dismay found the following blog entry which contradicts our experiment:

https://sciencenotes.org/why-a-glass-ball-bounces-higher-than-a-rubber-ball/

• here is a video related youtube.com/watch?v=bX8d0YTPvcY – anna v Oct 7 '18 at 15:19
• physicsforums.com/threads/… "If the ball is harder than the surface, the characteristics of the surface will be the most important for determining the bounce height, as it is the surface that will deform most. If the surface is harder than the ball, the reverse is true. – anna v Oct 7 '18 at 15:24
• If the ball and surface have the same hardness, then it will depend on the elasticity (energy-conserving properties) of the material, and the magnitude of the peak force. Most materials will be reasonably elastic if the force is below some critical value, the "plastic limit". If the force exceeds this limit, the object will lose significant energy via plastic deformation." – anna v Oct 7 '18 at 15:24
• you say you have laminate flooring on a table so the setup has a few areas where energy can be lost due to excessive motion. The glass ball needs a very hard and immovable surface to get its best bounce. – PhysicsDave Oct 7 '18 at 16:45

because the glass ball is stiffer than the laminate flooring, when it hits the floor it deforms the floor, thereby performing work on the floor and subtracting from the energy available to bounce the ball back. that work is lost because laminate flooring exhibits viscoelastic hysteresis which absorbs the work as deformation on short timescales but then releases that work on far longer timescales. So whatever springback you get out of the laminate flooring doesn't occur until long after the glass ball has exited the scene of the crime.

The main reason why in your case the rubber ball bounced higher ist the laminate flooring. If you had marble or granite the glass ball would habe bounced significantly better, even a bit better than the rubber.

On the laminate flooring the rubber ball can play out its flexibility, store energy in its own deformation and use it to bounce back up.

The glass ball on the other hand can't even deform much, because the floor is absorbing a lot of the impact. A good part of the energy will go into the deformation of the laminate. Most likely some of the deformation will remain and there should be at least a small mark on the floor. Often the laminated floor as whole can bend to a certain degree absorbing even more energy.
So if you want some nice bouncing you need to find a material that will not deform easily by the impact of the glass.

The rubber ball deforms very much in comparison to the glass ball, so on the peak of deformation a rather large part of the surface is touching the ground. The deformation results in friction and a relatively large area of adhesion, which are mainly responsible for the heat.
The glass ball on the other hand touches the ground on a much smaller area, so there is very little friction and most of the energy is consumed by the deformation of and absorbed impact by the ground.

• Also, the glass ball probably converted more KE into noise. – Keith McClary Nov 24 '18 at 3:00

There is a property of materials called the coefficient of restitution that is given by the relative velocity after a collision divided by the relative velocity before the collision. This coefficient is often denoted by e and comes from "Newton's Law of Restitution". This number is proportional to the height of an object as it bounces off the floor divided by the distance from which it was dropped. $$e = \frac{y_1}{y_0}$$ $$where\ y1\ =\ maximum\ height\ of\ ball\ after\ 1st\ bounce\ off\ floor$$ $$y_0 = height\ from\ which\ ball\ is\ initially\ dropped$$

A ball with a coefficient of restitution = 1 will return to the starting point when dropped. A hard rubber ball at room temperature has $$e \approx 0.9$$ while a glass ball has e between 0.65-0.7. Hence the rubber ball bounces higher. There are tables of values of e on the internet and in the Wikipedia reference given below.

Some useful references are here, here, and here.

I'm not sure why the paper you linked had the reverse answer. This reference has measurements for balls of different material and include a steel ball. Maybe the study done in the linked paper used a very soft rubber ball. All things being equal, a hard solid rubber ball ( think superball) will bounce much higher than a steel or glass ball.