1. Explain how inertia relates to mass
Day 1
Opening Activity:
Today I will:
Define momentum
Explain momentum in terms of inertia and velocity and change in momentum
Define inertia
Explain how inertia relates to mass

2. Chapter 7 - Momentum

3. Inertia – resistance to a change in motion Momentum –
inertia in motion (a moving object’s resistance to any change in its motion)
Momentum = mass X velocity
p = mv

4. How much momentum does a car sitting at a stop light have?
Zero!! None!! It is at rest so v = 0; p=mv

5. Inertia of car vs. truck truck – more massive; more inertia
car – small mass, less inertia

6. Which one has the greater momentum (car or truck)?
Can’t say!
How is it possible for the car to have more momentum then the truck? (what would we need to know)

7. We would have to look at the mass and the velocity of both!

8. What if we have a change in mass or in velocity?
If the mass or velocity changes (or both), so does the momentum
When we have a change in velocity over a time period what does that tell us?
accelerating (gaining or losing velocity over time)
What is the cause of an acceleration?
a net force
Start here 8th

9. Acceleration is greater
Recall from Newton’s Second Law the relationship between force and acceleration
Greater force
Acceleration is greater
means the object undergoes a greater change in velocity
momentum = mass X velocity;
a greater change in velocity will give a greater change in momentum

10. Change in p and change in v
Δp = Δ(mv) also can be written
Δp = (Δm)(∆v) or Δp = m(Δv)
Start here with 3rd and 6th

11. Increasing Momentum (start with small p end up with a bigger p)
To increase the p – apply the greatest force for as long as possible (greatest impulse—increasing both force and impact time)
When would this be something you would want?

12. Decreasing Momentum (big p to small p)
When would we want to quickly decrease momentum?

13. 7.2 Impulse changes momentum
Force: needed to cause a change in momentum
length of time the force is applied is also important;
A large force over a large time interval will also give a great amount of change in momentum
This change in momentum is called the impulse

14. Impulse – the change in momentum
Impulse is the applied force that causes a change in velocity and the time interval that force is applied
Impulse = force X time interval
I = FΔt
The greater the impulse the greater the change in momentum

15. Impulse = change in momentum
I = FΔt
Δp = Δ(mv)
Since I = Δp…
FΔt = Δ(mv)

16. vocab… Impact force – applied force (golf club)
The unit for impact force is the Newton (N)
Impact time – how long the force is applied (units = s)
Impulse = impact force X time
Units for impulse = Ns
Start with 3rd

17. Page 100 RQ 1-7

18. Why is the impulse the same for a car with airbags and a car without?
Why have airbags if the impulse is the same?

19. What does the following picture have to do with impulse?

21. Ft = Ft Car with air bags Impulse = Ft
Small impact on person force; large time
Car without air bags
Impulse = Ft
Large impact on person force; small time
Ft = Ft

22. Momentum Problem Packet: yellow

23. 7.3 Bouncing
Object comes into contact with another object and bounces off
In a bounce the impulse is greater, why??

24. Has a greater change in velocity!!
NOTE: if the object did not bounce it would hit the surface and stop

25. Opening Question: Today I will: Explain the conservation of momentum
Explain what it means to say that momentum is conserved
Identify different types of collisions
Change in momentum = impulse, how is it possible for the momentum to decrease but the impulse remains the same?
The answer is simple. The impulse = change in momentum. So the impulse equals the difference in the momentum from before the collision to after (pafter- pbefore).
Turn in impulse and momentum problem sheet from break!!!

26. 7.4 Conservation of Momentum
Forces causes acceleration
Impulse causes a change in momentum
An impulse is formed when an external (outside) force acts on an object
The external force causes the object to accelerate and to change momentum (Internal forces can’t do this…remember the horse and cart problem)
Start with 3rd 6th period

27. Example: Soccer ball
Ball has air inside, air pushes outward on ball and ball inward on air; this is an internal force
Will the air cause the ball to move?
No…some outside force must be applied

28. Newton’s First Law –
If an outside (external) force is not present, an object will NOT accelerate. (it’s velocity will remain constant)
If the object has the same velocity, there will not be any change in momentum.

29. Law of conservation of momentum
Conserved – when something remains the same; unchanged
In the absence of an external force (net force), the momentum of a system remains unchanged.
The net momentum can not be gained or lost.

30. Cannon and Cannonball Cannon exerts a forward force on cannonball
The cannonball exerts an equal force backwards on the cannon
Cannonball accelerates more because it has less mass (gains speed more quickly)
Cannon also accelerates but a lot less than the cannonball and in the opposite direction
Start here 3rd

31. In terms of impulse FΔt = m (Δv)
F and t is the same for both cannon and cannonball; so impulse is the same
The change in momentum each undergoes is the same (note: difference in mass and velocity)

32. Cannon and Cannonball in terms of momentum…
Before the cannon fires…the system is at rest…momentum = zero
Cannonball is then fired…
Cannonball has a positive momentum (moving forward)
Cannon has a negative momentum (moving backwards)
These momenta are equal but opposite
Overall momentum after firing = Zero!

33. Pc + PCB = PC’ + PCB’
= PC’ + PCB’
0 = PC’ + PCB’
-PCB’ = PC’

34. 7.5 Collisions law of conservation of momentum:
net pbefore collision = net pafter collision

35. 2 types of collisions
Elastic collision
Inelastic collision

36. Elastic Collision
Objects collide without being permanently deformed and without generating heat
Perfect elastic collision, colliding objects bounce perfectly
Conservation of momentum holds true
Turn to page 94

38. Inelastic Collision
Colliding objects become tangles or couple together
Conservation of momentum holds true even when colliding objects become distorted and generate heat
Freight train page 94
Start with 6th period on Thursday, April 5

39. Take out yellow problem packet
Read each problem and identify as elastic or inelastic for all conservation of momentum solved and practice exercises
Start w 8th

40. Opening Question: Today I will:
Explain what it means to say that momentum is conserved
Identify different types of collisions
Solve for conservation of momentum problems
What does it mean to say that momentum is conserved?
Have out yellow packets!!!
If you were not here yesterday, turn in your impulse and momentum worksheet!

41. Math Equations Psystem before = Psystem after Example for two objects
Before After
P1i + P2i = P1f + P2f
m1v1i + m2v2i = m1v1f + m2v2f
Note:
in an inelastic collision the final velocities are the same
Also possible for objects to start out together with same velocity and then to separate

45. Practice Exercises
7-10

46. Examples of Collisions
Crashes

47. Think and Solve A) 20, 000 Ns B) can’t solve without t 2000N
A) 16 Ns B) -32 Ns C) 64 N D) double the F
4 km/h
Case 1: 0.83 m/s case 2: m/s
100,000 m/s (that would be 224, 000 mi/h)

48. Problems on page 669 -1320N 0.5 N A) 500 Ns B) 500 Ns C) 500 N
Same as before explosion so 3 X 4 = 12 units