Momentum

1. Momentum and Impulse
Physics: In Motion

2. Momentum
https://www.youtube.com/watch?v=2UHS883_P60

3. Momentum
Newton combined the ideas of an object’s mass with its velocity and
calculated its motion.
He called this motion momentum.
Momentum is the quantity of motion an object has.
Momentum is a measurement of mass in motion: how much mass is in
how much motion.

4. Momentum
To bring an object to a stop, we must decrease the object’s momentum
to 0.

5. Momentum
Momentum is calculated according the the equation…
P = m•v
P = momentum (N•s or kg•m/s)
m = mass of the object (kg)
v = velocity (m/s)
∆P = m•∆v

6. What is the momentum of a 100 000 kg train moving at 5.0 m/s?
What is the momentum of a 100 kg train moving at 5.0 m/s?
How do their momentums compare?
Momentum Calculations

7. Momentum Calculations
What is the momentum of a 10 kg toy car moving at 5m/s?
What is the momentum of a 10 kg toy car moving at 10m/s?
How do their momentums compare?

8. Momentum Calculations
Calculate the momentum of cart 1 – 3.00 kg cart moving at 30 m/s North.
Calculate the momentum of cart 2 – 2.00 kg cart moving 45.0 m/s South.
Can you say their momentums are equal? Why or why not?

9. Momentum Calculations Recap
If velocity increases, the momentum will increase at the same rate.
If velocity decreases, the momentum will decrease at the same rate.
If mass increases, the momentum will increase at the same rate.
If mass decreases, the momentum will decrease at the same rate.
Heavier objects travelling at the same velocity will have more momentum.
Faster moving objects with the same mass will have more momentum.

10. Conservation of Momentum
By measuring the momentum of colliding objects before and after a collision,
Newton found.
The total momentum of any system is conserved.
P(total before collision) = P(total after collision)
m•v(total before collision) = m•v(total after collision)

11. Conservation of Momentum
Ex. If a school bus collides with a car, the total momentum before the collision
is equal to the total momentum after the collision (as long as there is no net
force acting on the system).

12. There are two types of ways the collision could
happen...
When the school bus and the car collide they can become one attached
wreck.
Momentum of bus (before) + Momemtum of Car (before) = Momentum of bus/car (after)
mbusvbus mcarvcar mbus/carvbus/car

13. There are two types of ways the collision could
happen...
When the school bus and the car collide they can become two separate
wrecks.
Momentum of bus + Momentum of Car = Momentum of bus + Momentum of car
(before) (before) (after) (after)
mbus1vbus1 mcar1vcar1 mbus2vbus2 mcar2vcar2

14. Car Crashes
https://www.youtube.com/watch?v=c0tlOPorrDw

15. Collisions
https://phet.colorado.edu/sims/collision-lab/collision-lab_en.html

16. What do you Remember about Momentum?

17. Momentum is the quantity of motion an object has.
Momentum is calculated by the following equation:
P = m•v
Momentum Recap

18. Momentum Recap
The total momentum of any elastic collision is conserved.

19. Conservation of Momentum
https://www.youtube.com/watch?v=4IYDb6K5UF8

20. Momentum Calculations
What is the final momentum, if a 4000 kg bus travelling at 80km/h
crashes into a car with a mass of 1000 kg travelling at a speed of 60
km/h?

21. Skateboard Momentum Examples
Throw a medicine ball while on a
skateboard.
What happens?
What’s happening with
momentum?

22. Conservation of Momentum Example
https://youtu.be/j1ugU_NwVLE?t=187

23. What can we do to reduce an object’s
momentum to zero?

24. We can apply an Impulse!
Impulse is the force acting on an object
and the time interval the force is
exerted.
Impulse is a vector quantity.

25. Impulse Calculations
Impulse is calculated by the
following equation
I = F • t
I = Impulse (N•s)
F = force (N)
t = time (s)

26. Impulse
Since impulse depends on both force and time, there is more than one way to
apply a large impulse on an object.
To increase the magnitude of an impulse...
1. You can increase the force applied
2. You can increase the length of time the force is being applied

27. Impulse Example
https://www.youtube.com/watch?v=K0ra7479zBs

28. Impulse Example Continued
The bedsheet had some ‘give’ to it. Thus, increasing the contact time and
distance and reducing the overall average force exerted on the egg.
The force of the egg is spread over the entire bedsheet and not just one
specific point.
This is the same idea as airbags

29. Impulse in Volleyball
How can you improve your spike? Improve your impulse!
1. Go to the gym to build up strength - this increases your force
2. Follow through your hit - this increases your contact time with the ball
Increase force + increase time = increase in impulse

30. Impulse Calculations
Impulse is also defined as the change in an object’s momentum.
Therefore, it can also be calculated according to any of the following
equations.
I = F•t
I = ∆P
I = m∆v
I = m(v2 - v1)

31. Impulse Calculations - Beginner
A force of 13N is applied to an object for 35s. What is the impulse acting on
the object?

32. Impulse Calculations - Intermediate
An object has a momentum of 1000 kg•m/s.
What is the impulse acting on the object in order for it to stop moving?
What force is needed to stop in 1 second?
In 2 seconds?

33. Impulse Calculations - Advanced
How many seconds would a force of 9.00 N have to act on a 3.00 kg mass in
order to change its velocity from 4 m/s to 8 m/s?

34. Impulse Calculations - Advanced
A 3.00 kg ball moving with an initial velocity of +4.00 m/s is acted upon by a
constant force F, for a period of 5.00 seconds. After the interaction, the ball is
moving with a velocity of – 6.00 m/s. Find F.

35. Momentum and Impulse Recap
When an unbalanced force acts on an object it will accelerate
A.k.a. it will change velocity - either speed up or slow down
When an object’s velocity changes, so does its momentum.
P = m•v
When something exerts a force on you, it exerts an impulse
I = F•t
Impulse changes Momentum and is also defined as I = ∆P

36. Cushioning the Blow
The impulse - momentum relationship is important to understand safety in
car crashes.
A 2000kg car driving at 50km/h has a lot of momentum.
To reduce that momentum to 0kg•km/h we must apply an impulse opposite
the car’s motion.
To do this safely we want to apply an impulse by exerting a force on the
wheels for a long period of time.

37. Cushioning the Blow
In a collision the impulse is applied in a short period of time that result in
destructive forces to the occupants.
To increase the length of time of an impulse during a car crash cars are
designed to have a “crumple zone.”
A crumple zone is a part of a car that is designed to compress during an
accident to absorb the impulse and increase the amount of time of the
impulse, thus decreasing the force in the impulse.
I.e. Crumple zones mean that the impulse is reduced before it is passed on to
the occupants in the vehicle.

38. Car Crashes
https://www.youtube.com/watch?v=r8E5dUnLmh4&t=61s
https://www.youtube.com/watch?v=kly5BM8G3iM

39. Crumple Zones

40. Egg Drop Instructions
Find a group of 2 or 3.
Create your own contraption to reduce the force of an impulse by increasing
the time of that impulse.
- The egg will be inserted into the contraption at the end and must be able
to be taken out after the drop to be inspected.
Answer the questions on the handout.
Prepare for the drop zone.