Using momentum to deal with collisions -- in 1-D, and 2-D

Last time, we learned how momentum was conserved in collisions between objects. Let's put that information to use in a real-word situation: short-track speed skating relays!

Using physics to win a relay race

Collisions in 2-D

All the examples we've seen so far involve motion in a single dimension: forward-and-back, or left-and-right. But in real life, most objects are free to move in at least two (if not three) dimensions. In order to play a good game of billiards, understanding the physics behind two-dimensional collisions is key.

A very nice billiard shot involving multiple collisions

In two dimensions, the total vector momentum is still conserved. That means that each component of momentum remains the same before and after the encounter.

I recommend building a table to help you keep track of the momentum before and after a collision.

Okay, let's try some examples.

Now, sometimes, you'll see situations in which it's not clear whether you ought to use conservation of energy, or conservation of momentum .... or maybe even BOTH. Learning which tool to use is a skill that only comes with practice and experience.

Little Billy at the water-slide park