# Chapter 11. Lesson 2

## Momentum

Momentum is the speed and the mass of something. It is like some people sledding down a hill and gaining speed as they go down. A baseball has more momentum than a tennis ball because a baseball has more mass.

## The 3 laws of Motion

The first law of motion is, if you are riding in a car but you hit a wall an unbalanced force stops you. For example, if you run into a chair-the chair stops you. The second law of motion is like bowling pins. The ball comes and knocks all the pins down. The third law of motion is about action and reaction forces. Like jumping down on the diving board is the action force and the diving board throwing you back is the reaction force.

## Gravity

Gravity is the earth pulling you to it so you wont fly off into space. For example, pretty much anything. Everything is being pulled to the earth like a book or a table. Space does not have gravity so if you went there you would just float.

## Weightlessness

Weightlessness means that you feel like you do not weigh anything, For example, if you were in space you would float. If you were on the moon you would weigh 6 times less your weight, so it is easier to jump and you could walk a lot farther in one step than you could on the earth.