Newton’s Laws of Motion

The First Law of Motion

Objects at rest will stay at rest and objects moving at a constant velocity will continue moving at a constant velocity.

WHAT???

• Objects at rest stay at rest.

• Objects in motion stay in motion.

WHY???

• A force must act on them to make them start or stop.

What forces change an objects motion?

• Friction

• Gravity

• A push or a pull

Inertia – the tendency for an object to stay at rest or in motion.

The Second Law of Motion

Acceleration (change in speed or direction) of an object depends on the object’s mass and on the net force acting on it.

10 N

Calculating Force

F= m x a

a = F ÷ m

What is the net force on a 1,000-kg object accelerating at 3 m/s2?

What net force is needed to accelerate a 25-kg cart at 14 m/s2?

Acceleration

Increase Force

OR

Decrease Mass

Acceleration

Decrease Force

OR

Increase Mass

The Third Law of Motion

For every action there is an equal and opposite reaction

15 N 15 N

momentum – the product of an object’s mass and velocity

momentum = mass x velocity

What is the momentum of a bird with a mass of 0.018kg flying at 15m/s?

A golf ball travels at 16m/s, while a baseball moves at 7m/s. The mass of the golf ball is 0.045kg and the mass of the baseball is 0.14kg. Which has the greater momentum?

Law of Conservation of Momentum – in the absence of outside forces, the total momentum of objects that interact does not change.