Here's a breakdown:

* Momentum = mass x velocity

* Mass: How much matter an object has. The more massive an object, the harder it is to change its motion.

* Velocity: How fast an object is moving in a specific direction. The faster an object is moving, the harder it is to stop.

Why is this hard to stop?

Imagine you have a bowling ball and a tennis ball. Both are moving at the same speed. Which one is harder to stop? The bowling ball, of course, because it has more mass. It has more inertia, meaning it resists changes in its motion.

The same principle applies to velocity. A car moving at 60 mph has more momentum than the same car moving at 10 mph. This is why it's harder to stop a car at a higher speed.

In essence: Momentum is a measure of how much effort it takes to stop an object that's already in motion. The more momentum an object has, the more force you need to apply to bring it to a stop.