Momentum and Inertia8SCIENCE

Matter in motion

• Matter is what all things in the universe are made from – atoms etc.

• The amount of matter is called mass– Usually in kilograms (kg)

• Mass is important:– Objects with a lot of mass are

hard to move and once they start moving, are difficult to stop

• This ability to stay still or stay moving is called inertia

Momentum

• Sir Isaac Newton was a scientist who developed the ideas of gravity and many laws of physics

• He decided mass and velocity are the two most important factors to know when describing motion

• He called this momentum:mass (m) x velocity (v) = momentum (p)m x v = p (momentum)

Momentum• Momentum includes velocity, which means it has a

direction– ex: if a ball is hit from a tennis racket and coming towards you,

you should move out of the way – even if you catch the ball, it will hurt your hand. This ball has momentum.

• Momentum points in the direction of motion, and an object can have positive or negative momentum depending on the direction

• Ex: What is the momentum of these balls?

B

Conservation of Momentum

• Law of conservation of momentum:– If no outside forces act on a group of objects, the

momentum of the objects will never change– If an object slows down, its because it has hit

another object and that hit object begins to move faster

– Ex. Billiards:– When you hit the balls in a rack the main

ball slows down when it hits the rest and the momentum is transferred, gaining an equal amount of momentum to travel across the pool table

Law of Conservation of Momentum