Newton figured out that if you know hard you push an object, and you know how massive it is, you can figure out how fast its speed changes. Saying the same thing, but using physics words: the force applied to an object equals the mass of the object times the resulting acceleration. Writing this as an equation, we say F = ma.
So if we know the forces on an object, we then compute the acceleration, and then we can then figure out how much its speed has changed.
The ancient Greeks thought moving objects had a natural tendency to slow down. Galileo and Newton, by experimenting, discovered that the reverse was true: objects in motion will keep moving, uness acted upon by an outside force. (This is also F = ma!)
If the Greeks had invented ice skating, they would have figured this out! When you push off on skates on clean ice, you'll glide for quite a while - the blades slide over the ice with very little friction. Eventually, the frictional forces will slow you to a halt. Too bad the Greek's lived in a temperate climate!
Back to the Physics of Ice Skating
by Karen Knierman and Jane Rigby