Transcript for Water Droplets Bouncing on Water!

You 'd think nothing exciting would happen. You'd think it would just go like this.

But what we'll see is much more interesting.

- Alright, let's drop it!

What we've got here are water droplets...

...which look pretty ordinary at normal speed.

But, at 2,000 frames per second...

Maybe mathematician John Bush can explain to us just how a drop can bounce.

So you're saying that that happens all the time?

That's right - everytime a water drop coalesces into water. So, everytime it rains.

That's raindrops in a puddle?

Yes, so that's billions of times a day.

Why does the droplet sit without just connecting?

There's an air layer in between the two, and basically it will coalesce as soon as the...

...drop makes contact with the bath.

But it takes a finite amount of time for the air layer to drain.

Or, for non-PhDs, there's a thin layer of air separating the drop from the water.

But as the air is pushed aside, most of the droplet connects with the water below.

But this happens so fast, the connection is actually pinched off,

and a smaller droplet is formed.

But why do some of the drops leap up into the air?

When it coalesces, waves are generated at the point of contact, and they sweep upwards...

...and they apply a force, which lifts the drops off the surface.

And then, once again, it's surface tension. It has enough force that it pulls itself back off.

This surface tension is the quality of a liquid that causes the surface layer of that liquid...

...to behave like an elastic sheet.

It's the effect that allows insects to walk on water...

...and water drops to hold together.

This cycle happens again and again,

until the droplet is small enough to be completely absorbed.