1. Momentum

2. Momentum Which is harder to stop a car or truck going the same speed?
How about a car going 100 mph or a truck going 10 mph?
Why?
Momentum is inertia in motion.
Defined as the product of the mass and its velocity.
Or Momentum = mass x velocity

3. Momentum continued When direction is not a factor:
Momentum = mass x speed.
We can see from this definition that an object can have a large momentum if the speed or mass is high.
A large ship moving at a slow speed has a large momentum.
A small bullet at a high speed has a large momentum.
If an objects velocity is 0 what is its momentum?

4. Impulse
If the momentum of an object changes, then either its mass or velocity changed or both.
Usually it is a change in velocity or acceleration.
What causes the change in velocity or acceleration?
Force.
When talking change in momentum time is important in addition to force.

5. Impulse and time
If you apply a certain force on a stalled car over a short amount of time you cause a change in the momentum of the car.
If you apply the same force over a longer time period you create a greater change in the car’s momentum.
So in change in momentum both force and time are important.

6. formula
Impulse = force x time interval

7. Impulse changes Momentum
The greater the impulse the greater the change in momentum.
Impulse = change in momentum.
Ft=∆(mv)
This is a relationship between the two.
Helps to analyze examples when forces act and motion changes.
Sometimes change in momentum can cause of impulse.

8. Increasing momentum
To increase the momentum of an object you would want the to apply the largest force possible for as long as possible.
Can you think of examples in sports where not only do you want to apply a large force, but you try to keep contact with the item?
Baseball, golf, soccer- in all of these the follow through is just as important as the force.

9. Average force
As a golfer swings his club the force involved changes from instant to instant.
Before there is contact the force is 0
Force then rapidly increases as the ball is distorted.
Force then diminishes as the ball speeds forward and returns to original shape.
When we speak of force in these situations we mean average force.

10. Decreasing momentum
If you were in a car that was out of control and you had two options:
1) hit a haystack or 2) hit a brick wall
Which would you choose and why?
It takes the same impulse to decrease your momentum to 0.
Same impulse does not mean same amount of force or same amount of time.

11. Impulse is a product of both force and time.
You want to extend the time of the impulse to lower the force.
Hitting the haystack extends the amount of time it takes to get you to 0 momentum.
Thus reduces the force.
If the time interval is extended 100 times, the force is reduced to a hundredth.
Protective gear in sports, airbags, are all trying to increase the time interval.

12. Why do you bend your knees when you jump off something?
You increase your landing time.
In what other situations do you extend the time of momentum change to reduce the force?

13. Decreasing momentum over a short time
If the time is short the force will be large.
If a boxer is being hit in the face what does he do?
What happens if he leans into the punch?

14. Bouncing
If a flower pot falls off a shelf onto your head you may be in trouble.
If the flower pot bounces off your head then you may be in more serious trouble. Why?
Impulses are greater when an object bounces.
Impulses required to bring the object to a stop and “throw it back again” is greater than the impulse required just to stop it.

15. Bouncing
This is the same as catching the pot and throwing it back up. This takes more energy from your hand than just to catch it.
A dart thrown at a wood block with a nail sticks and the block stays up right.
But a rubber ball on the end and you get it to bounce off causing the block to fall over.
Pelton wheel.