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## PowerPoint Slideshow about ' Momentum' - taipa

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Presentation Transcript

What’s the point?

- Nature keeps careful account of momentum.

Think Question

Which process will require more time?

- Pulling as hard as you can to accelerate a little red wagon from rest to a speed of 1 m/s.
- Pulling as hard as you can to accelerate a horse trailer from rest to a speed of 1 m/s.
- The two take the same amount of time.

Think Question

Which process will require more force?

- Accelerating a little red wagon from rest to a speed of 1m/s in ten seconds
- Accelerating a horse trailer from rest to a speed of 1m/s in ten seconds.
- The two take the same force.

Impulse = FDt

where

F Is net force

Dt is duration

ImpulseEffect of a force over time

Impulse is a vector.

Think Question

Two objects of different masses move at the same velocity. Which one is harder to stop?

The light object.

The massive object.

Think Question

Two objects with the same mass move different speeds. Which one is harder to stop?

The fast object.

The slow object.

Whiteboard Work

Prove that when a net force F is applied to an object of mass m for a time Dt, its change in momentum is

Dp = FDt

Poll Question

Which changes its momentum the most?

- A moving object that stops when it hits a barrier.
- A moving object that bounces back from a barrier.

Hints:

Momentum is a vector.

Which receives the greater impulse?

final p – initial p

final p – initial p

initial p

initial p

Dp

Dp

final p

final p= 0

Rebound and MomentumPoll Question

Which changes its kinetic energy the most?

- A moving object that stops when it hits a barrier.
- A moving object that bounces back from a barrier.

Hints:

Kinetic energy is a scalar.

Which has the greater net work done?

Poll Question

If a 0.25-g insect collides with a 1250-kg compact car, which experiences the greatest impulse in the collision?

The insect.

The car.

It’s a tie.

Insufficient information to answer.

Hint: Remember Newton’s third law.

Poll Question

If a 0.25-g insect collides with a 1250-kg compact car, which experiences the greatest momentum change in the collision?

The insect.

The car.

It’s a tie.

Insufficient information to answer.

Hint:Remember the impulse-momentum theorem.

Conservation of Momentum

- Newton’s first law:
- no outside force
- no change in v
- thus no change in p

- So an isolated object’s momentum never changes.

- ∑pi = ∑pf

- Newton’s third law:
- interacting objects apply equal and opposite impulses to each other
- they experience equal and opposite momentum changes

- So the sum of their momenta remains the same.

Conservation of Momentum

The total momentum of an isolated system never changes.

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