Linear Momentum

PhysicsMrs. Coyle

Linear Momentum, p

p= m v • Momentum is a vector.• The direction of momentum is the same as the

direction of the velocity of the object.• Unit: kg m/s or N s• “Inertia in Motion”

Question 1:

• What has more momentum, a dump truck at rest or a pebble moving down a hill at 1m/s?

Question 2

• How can you change the momentum of an object?

Impulse =

Impulse = p = m v = Ft

Problem 1

• Starting with Newton’s second law, show that for a constant force, p = m v = Ft .

To reduce the force of impact, increase the time of impact.

For a given change in velocity, p is constant :

Question 3:

• How do you have a better chance of winning in a water balloon toss contest?

Question 4:

• Why does a boxer “roll with the punches”?

Question 5:

• Why should you follow through in a serve when playing tennis, or when hitting a baseball?

Problem 2A ball at rest has a mass 0.5kg andis kicked with a force of 40N. Theimpact lasts 0.2s. Find:a)The change in momentum of the ball.b)The final velocity of the ball.

Answer: a) 8 Ns, b)16m/s

Problem 3

• A football player of mass 130kg travelling at 12.0m/s collides with another player and comes to rest in 0.90s. What was the force of impact?

• Answer:1,733N

Impulse is the area under the curve in a graph of F vs t.

F

t

Some Engineering Applications

Question 6

• Why are airbags used?

M

A

R

S

E

XPLORATION

MARS LANDER AIR BAGS

Rover Exits the Lander

Applications in Engineering Household Items

MILK BOTTLES

THE EGG CARTON