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# Collisions in Physics

When we think of collisions in physics, we are not just thinking about car crashes.

## Collisions or Interactions?

Really, we should think in terms of interactions. For example, in some common “collision” labs, we use carts that have magnets in them. The magnets are positioned so that they repel each other. Therefore, when the carts get close to each other, the magnets push them apart before they actually collide.

A commonly asked question in homework or test questions involves two stationary people on ice skates pushing off of one another. While no normal person would call this a collision or explosion, a physicist might. The reason is that we can treat this interaction the same way that we treat collisions, using the conservation of momentum.

## What Comes Next?

In this section, we will derive an equation for the conservation of momentum using the impulse momentum theorem. We will then solve a few problems using the conservation of momentum.