# Newtons' Laws

> **Up is always positive**

## First law

Constant velocity if forces are balanced
- object at rest remains at rest
- object at motion remains in motion
**only** if it does not experience an unbalanced force

## Second law
$$F_{net} = ma$$

## Third law

- Equal and opposite forces
- Normal force (reaction) is in opposite direction to action force

## Inclined plane

$$F=ma=mg\sin\theta-{\mathit{friction}}$$