Unpoppable Balloon
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Often, physics reveals that what seems to be the most likely explanation isn't always the correct one. (Remember that old theory about the sun moving around the earth?) Take something as simple as piercing a balloon with a pin. It's logical to assume that the balloon pops because air escapes through the hole. But as this simple experiment proves, there's something much more interesting going on.
What you'll need
- Latex balloon
- Clear tape
- Straight pin
How to play
Blow up a balloon and stick two 2-inch pieces of tape to the surface in an X.
Use the pin to puncture the balloon at the center of the cross. Even though you'll be able to feel air leaking through the hole, the balloon will stubbornly refuse to pop (at least for quite a while).
Watch the hole through the tape. It will widen into more of a crack (if it doesn't, try squeezing the balloon to help things along). When the crack nears the edge of the tape, the balloon will suddenly pop.
WHAT'S HAPPENING: When you puncture the balloon, it's not air rushing out the hole that causes it to pop. Instead, what actually occurs is something that physicists call a catastrophic crack propagation. The hole spreads, in effect ripping open the balloon. The tape, however, slows down the process dramatically, postponing the pop. If you think that's cool, consider this: when the tear in the balloon finally makes it past the tape, it starts to rip through the latex faster than the speed of sound. So that pop you hear is actually a sonic boom.
