| Description: |
A bowling ball is suspended from the ceiling of the lecture hall, becoming
the bob of a large pendulum. The lecturer takes the bowling ball and moves
back until the arc of the ball's swing is at the level of his nose. He
then marks the spot. If he then lets the ball go, when it swings back it
will just touch the tip of his nose. Remaining motionless when the ball
swings back toward you is difficult because the heavy bowling ball is moving
pretty fast at the bottom of its swing, and you knew that it's headed directly
for your nose. But, as energy is conserved, the ball can't possibly rise
higher than its original height. The gravitational potential energy put
into the ball by raising it to the height of your nose is converted into
kinetic energy of motion at the bottom of its swing. Of course, the taller
the lecturer the faster the ball travels at the bottom of its swing. Make
certain that the ball isn't pushed when released. |