You’ve all heard the expression “light as air,” right? It may seem as if air is a kind of nothingness, a weightless void in which we live and breathe. But air is much more forceful than it seems: according to the IRI Data Library, the average air pressure at the surface of the Earth is 14.7 pounds per square inch. So at any given moment, there are 14.7 pounds of air pressing down on a square inch of, say, your skin. And you don’t feel a thing!
But just how powerful is air pressure? That Physics Show loves to show off what is normally invisible– the joy of physics!– and they amazed us with a demonstration of air pressure’s effects. By taking the air out of a sealed tube, a vacuum (with no air pressure at all) is created. At one end of the tube is a row of three empty aluminum cans and at the other end is a ping pong ball. When Andrew punctures the seal, air rushes in and propels the ping pong ball with enough force through the tube that it crashes through all three aluminum cans! Would you believe me if I told you that the ping pong ball moves at 700 miles per hour through that tube? It’s true! That incredible speed is what allows the ball to puncture the cans.
That’s not the only incredible scientific discovery we made with That Physics Show in Episode 107. How much would someone have to pay you to lie down between two beds of nails, and how much more would you require for someone to stand on top of the whole apparatus? Sounds like a medieval torture device, doesn’t it?
In a segment I like to call “Clash of the Davids,” That Physics Show’s David Maiullo sandwiched himself between two beds of nails with Wonderama’s David Osmond standing on top. And no, David Maiullo did not emerge bloody and screaming: he was perfectly intact! It all has to do with distribution of force. If a person weighs 200 pounds and lies down on a single nail, that’s 200 pounds of force per nail, and a truly gruesome injury. If that same person lies down on a bed of 100 nails, there is only two pounds of force on each of the nails– not enough to puncture human skin. The more nails you have, the less force is put on each nail.
The science on these concepts makes perfect sense, but sometimes you still have to see it to believe it:
