### Net force

- the combination of forces acting on an object

* opposite forces or direction- subtract

* same direction- add

### Balanced force

- opposite forces acting on an object that cancel each other out

* Net force is always 0

*object does not move

*does not change velocity

### Unbalanced force

- unequal forces that act on an object

* net force is never 0

* changes velocity of object

### Newton's 1st law of motion

- An object at rest will remain at rest and an object in motion will continue moving in a straight line at a constant speed until an outside force acts against it.

### Momentum

- a measure of how hard it is to stop an object's motion

* depends on mass and velocity

* more mass= more momentum

* more velocity = more momentum

### Newton's 2nd law of motion

- An object's acceleration depends on the size and direction of the force acting on it and the mass of the object.

What affects acceleration?

1. size of the force

2. direction of the force

3. mass of the object

### Newton's 3rd law of motion

- For every action there is an equal and opposite reaction

* forces always act in pairs

* equal and opposite pairs