A friend sent me an email about a
wrecker that fell into the sea trying to recover a car. Another
wrecker was sent to rescure the first. It also fell into the
sea. Both wrecker drivers had over extended the load on their
booms. They had forgotten the old engineering principle about the
center of gravity. My Dad would show us boys this trick before I
ever started Elementery School. It's one of the most graphic ways
I know to teach the principles of how center of gravity works.
Press the tines of a fork onto a spoon. Slip a toothpick between
the fork tines at 90 degrees. Place the toothpick on the wet rim
of a large glass. (Real glass won't burn. Don't use plastic or
Strike a match and set fire to the end of the toothpick that extends
over the glass.
The toothpick will burn down completely until it touches the wet rim of
It will burn out leaving nothing but the charred edge of the toothpick
remaining to hold up the heavy fork and spoon.
It WILL NOT fall because the center of gravity is below and toward the
center of the glass.
The part remaining holding things up is no longer than the thickness of
the glass. Notice how the handle of the fork remains "afloat" not
touching. Nothing touches anywhere except the toothpick.
It's not magic, just grade-school science.