Section 2.4: Forces transfer momentum

• _______________ is a measure of mass in motion.

Vocabulary

momentum

If you throw a tennis ball at a wall, what would happen?

If you could throw a wrecking ball at a wall, what would happen?

So…why would a wrecking ball have a different effect on the wall than the tennis ball?

The wrecking ball will have more momentum than the tennis ball because the wrecking ball has more ____________!mass

It would bounce

back to you!

• Momentum is similar to inertia, because it takes into account an object’s ____________.

• Momentum is dissimilar to inertia because inertia does NOT take into account an object’s ________________ like momentum does.

mass

velocity

Thinking Question

• An increase in either mass or velocity ___________________ momentum.

• A decrease in either mass or velocity _________________ momentum.

increases

decreases

Calculating Momentum:Formula

Momentum = mass x velocity

p = mvp = momentum

m = mass

v = velocity

Calculating MomentumClass Example

• What is the momentum of a 1.5 kg ball moving at 2 m/s?

p = 1.5 kg • 2 m/s

p = 3 kg • m/s

Calculating MomentumClass Practice Problem #1

• A 3 kg ball is moving with a velocity of 1 m/s. What is the ball’s momentum?

p = 3 kg • 1 m/s

p = 3 kg • m/s

Calculating MomentumClass Practice Problem #2

• What is the momentum of a 0.5 kg ball moving 0.5 m/s?

p = 0.5 kg • 0.5 m/sp = 0.25 kg • m/s

• A ___________ is a situation in which two objects in close contact exchange energy and momentum.

Vocabulary

collision

As the second car bumps into the back of the first car the force pushes the car forward. Some of the momentum of the second car is transferred to the first car. At the same time the second car slows down because of the reaction force from your car. Therefore….

The first car ______ momentum from the collision, and the second car ________ momentum.

gains

loses

• If two objects involved in a collision have very different masses, which one will have a greater change in velocity?

The one with less mass will have a greater change in velocity!

Thinking Question

• The principle of ______________________ states that the total momentum of a system of objects does not change, as long as no outside forces are acting on that system.

Vocabulary

conservation of momentum

Momentum 2

Momentum 1

Momentum 2 Momentum 1

Forces in collision

Total momentum

Total momentum

The momentum of this car

is greater than the other

car. Their combined

momentum is the total

momentum of the system.

The forces on the two cars are are equal and opposite. Momentum is transferred from one car to the other during the collision.

Which of Newton’s Laws is this?

The momentum lost by one car was gained by the other car. The total momentum of the system remains the same as it was before the collision.

Is momentum a vector?

•Yes – it has both size and direction!

What happens to the momentum of a bowling ball

when it strikes the pins?

Some of the momentum transfers to the pins, but the total momentum remains the same!

Thinking Question

• In a game of pool, momentum does not appear to be totally conserved. What other outside forces are acting on the momentum system?

Friction!

• What is the overall momentum of a system made up of a 1 kg ball moving south at 2 m/s and a 1.5 kg ball moving north at the same speed?

P=1 kg • 2 m/s

P = 2 kg • m/s south

Really….A Hard Thinking Question

P = 1.5 kg • 2 m/sP = 3 kg • m/s north

Since they are in opposite directions you should subtract:

3 kg • m/s – 2 kg • m/s

Overall momentum = 1 kg • m/s north