2. Momentum and impulse
What is Momentum???
What is Impulse???

3. What has more Momentum?
A civic going down the highway at 30 mph or a semi going the same speed?
A civic going 30 mph or a civic going 60 mph?
A civic going 5 mph or a semi parked along the road?
What factors do you think affect the momentum of something?

4. MOMENTUM p = mv MOMENTUM: Proportional to both mass and velocity
Symbol: p
It is a vector quantity
SI Units: kg • m/s
or N•s
p = mv
Momentum = mass x velocity

5. Practice
How much momentum does 68 kg runner have when he is running at 8.9 m/s (20 mi/hr)?
How much momentum does a 2730 kg truck have when it is moving at 8.9 m/s?

6. Conservation of Momentum
The total momentum of a system remains constant unless acted on by an outside force!
  action/yt/watch?videoId=hTZI-kpppuw
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ction/yt/watch?videoId=W9EqU1_DXUw
More about this later!!!!

7. Momentum and Impulse Impulse-Momentum Theorem
Δp = J = FΔt or FΔt = mvf - mvi
Change in momentum (Δp) is called impulse (J).
SI units: N•s or kg•m/s
Changes in momentum depend on both the force and the amount of time over which the force is applied.
Impulse can also be calculated by Ft.
The Impulse-Momentum Theorem is another version of Newton’s 2nd Law

8. Momentum and Newton’s 2nd Law
Prove that the two equations shown below are equivalent.
F = ma and F = p/t
Newton actually wrote his 2nd Law as F = p/t.
Force depends on how rapidly the momentum changes.

9. Stopping Time Ft = p = mv
When stopping, p is the same for rapid or gradual stops.
Increasing the time (t) decreases the force (F).
What examples demonstrate this relationship?
Air bags, padded dashboards, trampolines, etc
Decreasing the time (t) increases the force (F).
Hammers and baseball bats are made of hard material to reduce the time of impact.

10. CRASH!!! These two cars both get into an accident with the same initial conditions and this causes both cars to stop abruptly. What safety features does the newer model have and how do they work to keep the passengers/car safe?
Car from 1960’s
Car from 2008

11. Practice OnE
A 65 kg passenger in a car travels at a speed of 8.0 m/s. If the passenger is stopped by an airbag in 0.75 s, what is the force on the passenger’s face?
Answer: 6.9 x 102 N
If the car does not have an air bag and the passenger is instead stopped in s when he strikes the dashboard, by what factor does the force increase?
Answer: F = 2.0 x 104 N so it is 29 times greater

12. PRACTICE TWO
A 1350 kg car has a velocity of 22.0 m/s to the north. When braking rapidly, it stops in 4.50 s.
What was the momentum of the car before braking?
What is the magnitude of the force required to stop the car?
Answers:
2.97 x 104 kg • m/s to the north
x 103 N

13. Homework
p.199/Practice A
p.201/Practice B
p.203/Practice C