A machine that never stops?
For twenty-seven years Dr. Coatsworthy Mothbold has been building an
automatic polka-dotting machine. It can paint polka dots on
anything—walls and windows, shirts and socks, even pretzels and
pancakes!
Best of all, the polka-dotter is a perpetual- motion machine! Perpetual
motion (puhr [pehch]{.smallcaps} u uhl [moh]{.smallcaps} shuhn) is
motion that goes on forever. So this machine, says Dr. Mothbold proudly,
will never stop!
All the parts of the polka-dotter create forces—pushes and
pulls—that make the other parts work. And as each part gets a push or
pull, it gives a push or pull to another part. So Dr. Mothbold is sure
the machine will keep running itself. Is Dr. Mothbold right?
No, he isn’t. No matter how carefully the polka-dotter is made, it
won’t keep running! While pushes and pulls will keep it going for a
while, other things will make it slow down. Friction is one of these
things. The wheels and belt rubbing against each other, the brushes
rubbing as they paint, and the bumping of the brushes on the paint lever
will make the machine go slower and slower. Finally, the automatic
polka-dotter will stop.
People have tried to make all kinds of strange machines that will run
themselves. But the friction that slows the machines down is always a
little stronger than the forces the machines make to keep themselves
running. That’s why perpetual motion doesn’t work— and never will.
