Indiana Jones and the Mystery of the Cracking Whip
Posted by drdavescience on March 3, 2008
Indiana Jones and the Raiders of the Lost Ark is my favorite movie. I was watching it (again), and a friend asked me why a whip makes that characteristic “crack” sound. As a reminder, below is a YouTube video montage of Indiana Jones’ favorite weapon.
Where does the sound come from?
When you move something through the air really fast, it typically makes a “whoosh” kind of sound. If you swing a bat very fast, you can hear this sound. This is just the air moving around the bat. Cars and planes also make their own “whoosh” kind of sound, but no “crack” sound.
The distinctive whip “crack” sound occurs when the tip of the whip is moving at supersonic speeds.
This means that the tip of the whip is breaking the sound barrier! Isn’t that cool!
A similar sound is made when a fighter jet breaks the sound barrier. Check out this You Tube video of a fighter jet breaking the sound barrier.
I mentioned that only the tip of the whip moves at supersonic speed. As Indiana swings and snaps the whip, all of the energy of motion moves down to the tip and causes it to changes directions rapidly. When done properly, it cracks.
-Dr. Dave
