 |
A skateboarder launches
straight into the air from the top of a ramp. Seeming to hang in place
for just a moment, he turns in midair and directs himself back down the
ramp. Skaters call this maneuver a frontside
180. Physicists call it impossible.
Well, they don’t really call it impossible. Just very, very sneaky.
You see, one of the
fundamentals of physics is a little something called the law of conservation
of angular momentum. This is what it says: If you’re rotating, you’ll
keep rotating unless a twisting force, or torque, acts to stop you. Likewise,
if you’re not rotating, you can’t rotate unless a torque starts
you rotating. Seems fair enough, right? There’s just one more important
detail. If you’re in midair, the only force that can act on you is
gravity. On earth, gravity can’t make you rotate; it can only make
you fall. So the question is, how does a skater go from not rotating to
rotating, without the help of an external force?
 |
As it
turns out, skaters rotate in midair using a trick borrowed from housecats.
This simple experiment will show you how -- and why -- it works.
