What if nothing could bounce?

Drop a ball. Boing! It bounces back up.

Drop a lump of clay. Splat! It just stays there. What if everything were like the clay?

Drop a rubber ball and it bounces. Drop a lump of modeling clay and it lands with a splat and stays put. What makes the difference?

The ball squashes when it hits the floor, then springs back to its shape, pushing itself up. The clay squashes and stays squashed. This lab is a thought experiment: what if everything behaved like the clay, and nothing could spring back?

A bounce is a short collision in which an object deforms, stores energy and then returns much of it as it recovers its shape. OpenStax describes collisions in which internal kinetic energy is conserved as elastic, and those in which it changes as inelastic; when objects stick together, the loss is greatest.

This thought experiment removes elastic recovery from every material and follows three threads: ball games, sound reflections and springs.

Our world is full of bouncy things.

Balls bounce. Springs spring back. When you shout in a big hall, your voice can bounce back too!

Bounces are everywhere. Balls bounce in games. When you wind up a toy, you squeeze a spring that stores energy and later lets it out, OpenStax explains. Car springs squash when someone climbs in and push back up.

Even sound bounces. The National Park Service explains that bats send out sounds that bounce off objects and come back to their ears, which helps them find their way and their food.

OpenStax notes that winding a toy, an egg timer or an old-fashioned watch does work against a spring and stores energy that is recoverable as work, PE = ½kx² for a spring obeying Hooke's law. A ruler bent and released oscillates because a restoring force returns it toward equilibrium.

Waves bounce too. NOAA's active sonar sends a pulse into the water; if an object is in the way, the sound bounces off and returns as an echo, and the delay gives the range.

Now imagine nothing can bounce.

A dropped ball might go splat and stay down. Springs might stay squashed. Calm and quiet, but strange!

Imagine every material behaved like clay. A dropped ball might land with a thud and stay on the floor. A trampoline might feel like a soft mat. A squeezed spring might stay squeezed, so wind-up toys and old-fashioned wind-up watches might not work.

If sound could not bounce either, a big hall might not echo, and bats might have a much harder time finding their way. These are ideas, built from how bouncing works in our world.

With elastic recovery removed, every impact might be perfectly inelastic: the energy of motion might go entirely into heat, sound and permanent deformation, with nothing to return it. Springs might no longer store recoverable energy, so spring-driven devices and suspensions might lose their function.

Sound reflection is a different kind of bounce, the reflection of a pressure wave at a boundary, but the thought experiment removes it too. The consequences are reasoned ideas, not predictions.

A bouncy ball squashes when it hits the ground. Then it pops back into shape and pushes itself up.

Clay squashes too, but it does not pop back. So it does not bounce.

When a ball hits the ground, it squashes, like a squeezed spring. A University of Illinois physics answer explains that the squashing stores energy in the rubber, and the ball gives it back as it becomes round again, which sends it back up.

No bounce is perfect. OpenStax explains that when a rock is dropped on the ground, its energy turns into heat, sound and a dent in the ground, so it does not bounce at all. Even a bouncy ball never gets all its energy back: some becomes heat, so the ball warms up a little, and some becomes sound.

Elastic materials store energy as they deform and return it as they recover, following Hooke's law, F = −kx, for small deformations. OpenStax contrasts this with a rock dropped onto the ground, stopped by nonconservative forces that dissipate its mechanical energy as thermal energy, sound and surface distortion.

In an inelastic collision internal kinetic energy changes; in a perfectly inelastic one the objects stick together and kinetic energy falls to the minimum momentum conservation allows. A world with nothing bouncy would make every collision like that.

Bats use bouncing sounds to find bugs to eat.

Ships bounce sounds off the sea floor to learn how deep it is.

Some of the most useful bounces are sound bounces. Bats find insects by listening to echoes of their own calls, the National Park Service explains. NOAA uses sonar, which sends sound into the ocean and listens for the echo, to map the sea floor and find shipwrecks.

Springs matter too. OpenStax uses a car's suspension as an example of springs that squash when someone gets in and push back.

NOAA scientists use sonar to make nautical charts, locate hazards and map the seafloor; active sonar measures the time between a pulse and its echo to find range. Bats produce ultrasound whose echoes they recognize (National Park Service).

OpenStax uses a car's suspension as a Hooke's-law example: an 80 kg person climbing in settles the car by 1.20 cm. Without elastic recovery, both echolocation and spring suspension would lose their working principle.