Did you see what happens if you lift a ball and let go of it so that it hits the other balls?
Yes, that’s right! A ball jumps off the other end of the row. When it falls back, the same thing happens again, but this time at your end. With each collision, the motion of the first ball is passed on to the next ball in line, and so on to the last.
The amount of motion or ‘momentum’ of the balls decreases a little each time, though. Each time, part of the energy is converted into sound (the click that you hear) and into heat (through friction with their suspension points, the other balls and the air). That’s why the balls stop moving after a while.
Tip: Try letting go of several balls at the same time.
You will then see the same number of balls jump off at the other end. For example, if you let two balls go, the motion will be passed to the next two balls in line, and so on until the last two.
Testing out momentum for yourself using balls
Take a tennis ball and a volleyball. Drop them one at a time. How high do they bounce?
Now hold up both balls in the air, touching each other, with the tennis ball on top. If you drop the balls on the floor at the same time, the volleyball strangely stays on the floor and the tennis ball bounces up much higher.
This happens because the volleyball wants to bounce back up. But the tennis ball is in the way. The volleyball therefore transmits its momentum to the tennis ball that is just above it.
Momentum in snooker
In snooker you are only allowed to hit one ball with the cue. This ball must in turn hit the other balls and pass on its momentum.