1. Impulse, Momentum, and Collisions

2. Impulse, Momentum, and Collisions
Sections Covered – Physics
Chapter 7: pages 86 – 99
*Chapter 10: pages
Topics Covered
Linear Momentum
Impulse
Conservation of Momentum
Collisions
Elastic
Inelastic
Total inelastic
*Center of Mass

3. *Review What is inertia?
How much resistance an object has against a change in motion.
Mass = numerical amount of inertia
Large mass = lots of resistance
Small mass = not a lot of resistance

4. Momentum
Momentum is a quantity of movement or a measurement of how difficult it is to bring an object to a stop.
Two Kinds of Momentum:
Linear Momentum-
Momentum in a straight line
Angular Momentum-
Rotational or Circular Momentum

5. Linear Momentum p = linear momentum m = mass SI Units: v = velocity
Linear momentum is a vector that points in the same direction as the velocity. v p

6. Which Has More Momentum?
A truck with a mass of 9000 kg moving 50 m/s? OR
A moped with a mass of 180 kg moving 10 m/s?

7. Impulse
For a constant force, the product of the force and time over which the force acts is the Impulse
J = Impulse
F = force
SI Units:
Δt = time of contact
Impulse is a vector with the same direction as the force applied. F J

8. Impulse-Momentum Theory
The impulse exerted on an object changes the momentum of the object.
The larger the impulse, the greater the change in momentum

9. Conceptual Question
When you fall a significant distance and hit the ground, why do they tell you to tuck and roll when you hit the ground rather than just landing right on your feet?

10. Defining the System – Internal vs. External Forces
Define your system (in this chapter – this will normally involve 2 objects)
Any forces acting within your define system are internal forces
The two skaters above are in a closed system

11. Defining the System – Internal vs. External Forces
Forces that act on an object outside of the defined system are called external forces
Examples:
Case 1:
Meteor = External Force. Outside of the system
Case 2

12. Defining the System – Internal vs. External Forces
Forces that act on an object outside of the defined system are called external forces
Examples:
Case 1:
Meteor = External Force. Outside of the system
Case 2
Earthquake= External Force. Outside the system – changes how the problem is evaluated

13. Conservation of Momentum
The total momentum of an isolated or closed system remains constant.
Isolated/Closed Systems – systems with only internal forces, no external
Total Initial momentum = Total Final Momentum
Two Object Conservation of Momentum (For Objects 1 and 2):

14. Conservation of Momentum
For two objects, object A and object B:
Example: A B
mA = 2.3 kg
vAo = 1.4 m/s
mB = 0.8 kg
vBo = 0 m/s
vAf = 0.2 m/s
vBf = ? m/s

15. Warm-Up #1
A tennis player places a 55.0 kg automatic ball machine on a virtually frictionless tennis court. Both the machine and tennis balls inside are initially at rest. The machine fires a kg tennis ball with a positive velocity. The machine moves backwards with a velocity of m/s. What is the velocity of the tennis ball?
What are the two objects in this system?
vf = 36.0 m/s

16. Warm-Up #2
An ice skater (mass = 65.0 kg) moving to the right with a velocity of 2.50 m/s, holding a snowball (mass = kg) which is moving with the skater. She then throws the snowball with a velocity of 32.0 m/s with respect to the ground. What is the velocity of the skater after she throws the snowball?
What are the two objects in this system?
vf = 2.43 m/s

17. Warm-Up #3
A boy on a skateboard is initially at rest holding an 8.00 kg jug of water. He tosses the water, giving it a positive velocity of 3.00 m/s. The boy and skateboard move backwards with the magnitude of their velocity being m/s. What is the mass of the boy and skateboard together?
What are the two objects in this system?
m = 40.0 kg

18. Collisions!! Three different kinds of collisions
IMPORTANT: In ALL collisions, momentum is conserved.
Elastic Collisions
Inelastic Collisions
Total Inelastic Collisions

19. Collisions! Elastic Total Inelastic Inelastic
Perfect rebound, no energy loss
Some energy loss
Objects are stuck together after collision
Momentum conserved
Momentum conserved
Momentum conserved
KE conserved
KE NOT conserved
KE NOT conserved
KEo = KEf

20. Collision Summary YES YES NO YES NO YES Collision
Kinetic Energy Conserved
Momentum Conserved
Elastic Collision
Inelastic Collision
Total Inelastic Collision
YES
YES NO
YES NO
YES