# Eli5: What determines whether an object can bounce or not?

31 views

Is the material an object is made out of more important? Or also what material the ball comes into contact with also important? (throwing a ball down on concrete vs throwing it on grass)

In: 17

Have you heard of the term “dead cat bouncing”?

The idea is that if you drop *anything* from high enough, it will bounce at least once.

Elasticity. The material has to deform to convert the kinetic energy of its movement into potential energy in the deformation (like a spring) and then give the energy back to push the object back up. A high elasticity means that more of the energy that is absorbed by the object deforming comes back out as kinetic energy. Low elasticity means more of the energy is converted to another form like heat or breaking the internal structure of the object.

Lot of partial answers here that dont paint the complete picture. When something bounces it is transferring its movement into the object it hits and that object reflects that energy back.

Look at a newtons cradle for an example. When a single ball swings, that movement energy is transferred into the object it hits. That object will then move until it hits the next object transferring its energy like the first ball. This carries through all the balls until the final one has nothing to hit and carries through the air until it repeats the process in the other direction.

Now take a ball from each end and drop them at the same time. As the balls collide and transfer their energy inwards, they run into the other force that is traveling in the opposite direction. Since both balls have the same energy level, one is unable overcome the other. Now you have 2 balls pushing against each other with a ton of energy stored up that has to be used. Unable to overcome the opposing force, the energy gets reflected. Due to the construction of the newtons cradle and it’s suspension wires, that energy is contained to a single axis so that energy is reflected back in the direction it came from.

Now let’s scale this up to the real world, You have 2 objects to throw and 2 surfaces to throw them at. The objects are a golf ball and a wadded up T-shirt. The surfaces are a giant fluffy pillow and a massive brick wall.

You throw the golf ball at the brick wall and it bounces as expected. Tshirt at the pillow and the T-shirt falls to the ground. Now let’s throw the golf ball at the pillow and see what happens. As the golf ball collides with the pillow, that energy is transferred into the pillow. The pillow takes that energy and its gets used to move every individual fiber out of the way of the golf ball as there is nothing for the energy to transfer into and get reflected back at the golf ball. As a result the ball falls to the ground having lost all of its energy. T-shirt at the brick wall and the same thing happens bit the other way around. The energy of the T-shirt is lost as it collides with the wall because the fibers are not able to take that energy without using it to move out of the way.

While thing may paint the picture of that harder things always bounce and while that’s true to an extent, the final price of the puzzle is energy efficiency. This is often ascribed as things like elasticity, COP, etc and is the thing that rules most physics equations. The more energy an object uses without transferring it, means the less energy is available to get reflected back.

Pretty sure bouncing also takes into account the inverse, non-elastic hitting an elastic surface like a trampoline.

No reason you can’t create a soft sprung surface that would bounce an egg.

It would not have the elasticity to support anything bigger thou which would snap it.