Thursday, October 21, 2010

Big stones fall faster

The NY Times science section explains:
Q. I’ve heard that if a penny is dropped from the Empire State Building it could kill someone. But what about hail? It’s often much larger and falls from much higher, so why do I never hear about any deaths caused by it?
No, the penny will not kill anyone, as explained here and here.
The friction with other precipitation deforms a hailstone from a perfect sphere, making its velocity hard to calculate when it does become heavy enough to fall to earth. One estimate is that a half-inch stone falls about 30 feet a second, while a three-inch stone falls nearly 160 feet a second.
Occasionally I hear someone tell how Galileo's Leaning Tower of Pisa experiment proved Aristotle wrong about heavier rocks falling faster. Well, as the story explains, bigger hail stones do fall faster than smaller ones.

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