and I don't mean some digital depiction of a clap. I mean that when this man's

hands come together you're going to see something that is normally invisible.

You're going to see the actual sound wave leaving his hands and

traveling outward at 761 miles per hour --

the speed of sound!

And here it is again.

How is this possible?

Well, I'll start the explanation not with sound but with the heat

from a lighter. There's a puff of butane, sparks fly,

and the fuel ignites. But that shape billowing up from the flame isn't smoke --

That's normal air that has been expanded by heat.

We're able to see the density change thanks to a technique called

Schlieren Flow Visualization. Here's how it works.

You start off with a light, shining through a single slit.

If you reflect that light of a parabolic mirror all the rays become parallel

and then you can use another parabolic mirror to refocus the light down to a single focal point

and then in through the lens of a camera to make a picture.

Now here's the trick -- you place some sort of barrier right at the focal point.

Now you add something that will distort the air -- like a candle.

The candle will block light rays making a silhouette, and the flame will make light.

But rising heat will change the density of the air above the lighter

and that will bend the light rays. The bent light ray won't pass through the focal point.

it will be blocked by the barrier ... and the picture will be darker.

This technique can be used to see anything that distorts the air.

The heat from a hair straightener for example.

Even the heat coming off a human hand.

Epidemiologists used to study sneezes and coughs.

Engineers use it to study aerodynamic flow.

And sound? Well -- that's just another change in air density.

A traveling compression wave. So Schlieren Visualization

along with a high speed camera can be used to see it as well.

Here's a book landing on a table.

The end of a towel being snapped.

A firecracker.

An AK-47.

And of course, a clap.