Supersonic Flight


Find out how a whip and a Slinky can help us understand the speed of sound. 


Hi my name is Dan, and I'm an Explainer here at the National Air and Space Museum's "How Things Fly" gallery. Today we're gonna be learning about supersonic flight.

What is supersonic flight and what causes a sonic boom? Well, let's figure that out. Supersonic flight happens when an airplane reaches the speed of sound. The speed of sound is approximately 760 miles an hour. At 760 miles an hour air compresses, shockwaves form on the wings, and drag increases dramatically.

Here at the Museum, we have lots of supersonic aircrafts. If you look behind me, this airplane right here — the Lockheed Martin F-104 flies at Mach 2 or twice the speed of sound. The Bell X-1 was the first aircraft to fly the speed of sound and the North American X-15 is the fastest aircraft in the world.

Right here, I have a Slinky and we're going to use this to demonstrate how sound moves through air. When I pull the Slinky out, if I move one end, a wave is created and it goes to the opposite end of the Slinky. When I talk, I disturb the air and waves travel through the air until you hear them, so let's see.

[Dan wiggles one end of the slinky and a wave moves through the slinky to the other end.]

[Slinky rattles]

Did you see that?

[Slinky rattling] The wave is created on one end

[Slinky rattling] and travels all the way through the Slinky

[Slinky rattling] to the opposite side.

Supersonic airplanes aren't the only thing that create a sonic boom. In fact, we can create a sonic boom in this room right now. Let's take a look. Right here, I have a whip. Now let's see what happens.

[whip cracking]

Did you hear that? At the end of the whip, this part right here is called the "cracker". Notice how to whip tapers as we get closer to the cracker as mass decreases of velocity increases. That cracking sound you hear is when the cracker hits the speed of sound at 760 miles an hour causing the sonic boom that we hear.

Categories: Aerodynamics