1. Chapter 5
Momentum

2. Momentum inertia and motion Newton’s “quantity of motion”
helps us understand collisions and explosions

3. Momentum Momentum = mass ´ velocity p = mv
Momentum is a vector quantity.

4. A large truck has more momentum than a car moving at the same speed because it has a greater mass.
Which is more difficult to slow down? The car or the large truck?

5. P = mv P = mv Large Momentum Examples:
Huge ship moving at a small velocity
High velocity bullet
P = mv
P = mv

6. Impulse
In order to change the momentum of an object you must apply a force over some time interval.
Impulse = Force ´ time interval
= F t

7. Impulse and Momentum Impulse = Change in Momentum
= Final (mv) Initial (mv)
F t = D(mv)

8. Examples: Air bags in cars. Catching an egg. Boxing
Catching an egg.
Boxing

9. Conservation of Momentum
This means that the momentum doesn’t change.
Recall that F t = D(mv)
In this equation, F is the "external force".
Internal forces cannot cause a change in momentum.

10. Examples
Conservation of Momentum: If there are no external forces, the total momentum for a system remains unchanged.
Example 1: a person sitting inside a car pushing against the dashboard
Example 2: a bullet fired from a rifle
Example 3: a rocket is space

11. Question Which has more momentum? (A) A parked cruise ship
(B) You in your vehicle driving home

12. Clicker Question 3. Which of the following is true about momentum?
(a) it is a vector
(b) it is a product of mass times velocity
(c) impulses are required to change it
(d) all of the above

13. Chapter 6
Energy

14. Energy Universe is made up of matter and energy.
Energy is the mover of matter.
Energy has several forms:
Kinetic
Potential
Electrical
Heat
etc.

15. Work
Now instead of a force for how long in time we consider a force for how long in distance.
Work = Force ´ Distance
W = F d
The unit for work is the Newton-meter which is also called a Joule.

16. How much work?
A weight lifter lifts a barbell weighing Newtons 1.5 meters
A weight lifter pushes on a wall with a force of Newtons for 15 sec?

17. Power
Power is equal to the amount of work done per unit time.
The unit for power is the Joule/second which is also called a Watt.

18. Light Bulbs and Appliances
How much energy does a 100 Watt light bulb use in one hour?
How about a 40 Watt light bulb?

19. Mechanical Energy
When work is done on an object, the object generally has acquired the ability to do work.
This "ability to do work" is called energy and it has the same units as work….Joules.
Two Types of Mechanical Energy
Potential Energy and Kinetic Energy

20. Potential Energy The energy that is stored is called potential energy.
Examples:
Rubber bands
Springs
Bows
Batteries
Gravity

21. Gravitational Potential Energy
PE = Weight ´ height
PE = m g h
Question:
How much potential energy does a 10kg mass have relative to the ground if it is 5 meter above the ground?

22. Kinetic Energy
Kinetic Energy is the energy of motion.
Kinetic Energy = ½ mass ´ speed2
Question: How much kinetic energy does a 1kg mass have if it is moving at 10 meters/second?

23. Work/Energy Relationship
If you want to move something, you have to do work.

24. Conservation of Energy
Energy cannot be created or destroyed...
...it may be transformed from one form into another...
...but the total amount of energy never changes.
Demos
Galileo's incline
Bowling ball pendulum

25. Pendulum Example Problem
At what point is the kinetic energy the highest?
(A) At the bottom of its path
(B) At the ends of its path
(C) Somewhere in between

26. Pendulum Example Problem
At what point is the potential energy the highest?
(A) At the bottom of its path
(B) At the ends of its path
(C) Somewhere in between

27. Example Problem
A 100 kg mass is dropped from rest from a height of 1 meter.
How much potential energy does it have when it is released?
How much kinetic energy does it have just before it hits the ground?
What is its speed just before impact?
How much work could it do if it were to strike a nail before hitting the ground?

28. 100 kg
1 meter
100 kg
100 kg
nail

29. Comparison of Kinetic Energy and Momentum
Kinetic energy is a scalar quantity.
Momentum is a vector quantity.

30. A 1 kg mass is lifted 1 meter
A 1 kg mass is lifted 1 meter. The change in potential energy of the weight is
(a) 1 N (b) 9.8 N (c) 1 J (d) 9.8 J (e) 9.8 m/s2

31. End of Chapter 6