Momentum• All objects have mass; so if an object is

moving, then it has momentum - it has its mass in motion.

• The amount of momentum which an object has is dependent upon two variables:

– how much matter is moving?

– how fast the matter is moving?

• Momentum: "mass in motion”• Equation: p = m x v• Unit: kg*m/s

Momentum

• Momentum is a vector quantity.

Momentum

Consider a Mack truck and a roller skate moving down the street at the same speed. The considerably greater mass of the Mack truck gives it a considerably greater momentum. If the Mack truck were at rest, which would have the greater momentum?

If an object is at rest, the momentum of that object is “0” because there is no mass in motion.

Momentum Questions

1. Determine the momentum of a ...

a.) 60 kg halfback moving eastward at 9 m/s.

b.) 1000 kg car moving northward at 20 m/s.

c.) 40 kg man moving southward at 2 m/s.

p = 540 kg*m/s, east

p = 20,000 kg*m/s, north

p = 80 kg*m/s, south

Momentum Questions

2. A car possesses 20,000 units of momentum. What would be the car's new momentum if ...

a.) its velocity were doubled b.) its mass were doubledc.) both its velocity and mass were

doubled

p = 40,000 units

p = 40,000 units

p = 80,000 units

If the boulder and the boyhave the same momentum,will the boulder crush the boy?

Hint:  think about the momentum formula!

p = mv

DEMONSTRATIONS

• Egg and the Blanket

• Bowling Ball

IMPULSE – A force applied for a period of time which results in a change of momentum.

Impulse = change in momentum

F∆t = ∆p = ∆(mv)

F∆t = mvf - mvi

F∆t = m (vf – vi)

To change the momentum of a body, a force must be applied to the mass. The longer this force is applied to the mass, the greater effect it will have on changing the momentum.

The Wall The Haystack

Impulse

• A change in momentum in a short time requires a large force.

• A change in momentum in a long time requires a small force.

Greatest velocity change?Greatest acceleration?

Greatest momentum change?Greatest Impulse?

Therefore, a larger Force and impulse occurs!

Before the space shuttle lands, why

does it take giant S curves?

To increase landing time and decrease the force of the landing

1. An 80 kg skier loses control and demolishes a snow bank. If it takes the skier 3 seconds to come to rest from an impact speed of 9 m/s, find:

(a) the impulse on the man

(b) the average force exerted on him by the snow bank

-720 kg*m/s

-240 N

Lab Activity

Materials

dynamic cart

force sensor

motion sensor

Plot and calculate Impulse

Plot Fvs t graph

plot v vs t graph

Area is equal to impulse

change in momentum is equal to impulse

F vs t graph

• Area under the curve

7500

t (s)

20

F (N)

• Constant F

• Find Area:

=L x W

= F x t

= 7500 x 20

= 150,000 Ns 10

Impulse from an F vs t graph

• Area under the curve

7500

t (s)

20

F (N)

• Impulse = ∆F * t

• Find Area:

= 2(1/2 *b*h)

= 2(1/2*10*7500)

= 75,000 Ns10