MomentumBy: Heather Britton

Momentum•Momentum is a product of an objects

mass and velocity•Momentum is a vector quantity which

means it has both magnitude and direction

•The magnitude is the number•The direction is the same direction as

the velocity

Momentum

•p = mv•v = velocity (measured in m/s)•m = mass (measured in kg)•p = momentum (measured in kgm/s)•momentum is a lower case p and

power is a capital P

Example 1

•How much momentum does a 300 g snowball have when thrown with a velocity of 15 m/s?

Momentum•A fast moving car has more momentum

than a slow moving one of equal mass•A large truck has more momentum

than a small car moving at the same speed

•When considering momentum both mass and velocity must be taken into account

Momentum

•Newton’s second law was first described in terms of momentum

•The rate of change of momentum of a body is equal to the net force applied to it

•Recall rate means divided by time

Momentum•ΣF = Δp/Δt

•F = ma

Example 2

•What is the change in momentum when a 15 g rubber ball is dropped from a height of 1.5 m and bounces off the floor with a velocity of 3.5 m/s?

Impulse

•The sum of all forces is equal to the change of momentum divided by the change in time

•ΣF = Δp/Δt•Rearranging this equation we get the

definition of impulse•FΔt = Δp

Impulse

•The change in momentum is equal to the impulse applied to the object

•Force is not applied uniformly, therefore the average force must be used

Impulse

•Real life examples of how force is reduced include:•Bending your knees when landing

after jumping•Air bags in cars

•In both of these examples time in increased, therefore force in reduced

Example 3•A 0.144 kg baseball is pitched horizontally at

+38 m/s. After it is hit by a bat, it moves horizontally at -38 m/s.

•What impulse did the bat deliver to the ball?

• If the bat and ball were in contact 0.80 ms, what was the average force the bat exerted on the ball?

•Find the average acceleration of the ball during its contact with the bat.