1. Energy, Work and Power

2. Energy and Work Energy is the ability to do work
Ex. Kinetic, Thermal, Gravitational, Elastic, Chemical, Electric, Magnetic, Radiant…
Work is the transfer of energy

5. James Prescott Joule (1818 – 1889):
English physicist
Discovered relationship btw. heat & mechanical work (energy)
Conservation of Energy Theorem

7. Pg 218

8. Power Power is the rate at which work is done [N.m] ,[J] Joule
Pg. 241 #23, 24, 28
[W] watt
[s] second
James Watt (1736 – 1819):
Scottish inventor/mechanical engineer.
Improved the efficiency of steam engines.
Introduced horse power (750 watts).

9. If a hair dryer does 3000 J of work to heat the air every two seconds, what is its power?

10. A kg mass is placed on a forklift that can generate 950 W of power. What is the constant speed of the forklift while lifting this load?

11. A HD TV consumes 5.0 kW∙h of energy in 30 minutes.
What is its power?
How much does it cost to watch TV for hours if the cost of electricity during peak time is $0.12/ kW∙h

12. Mechanical Energy

13. Mechanical Energy is a combination of two fundamental types of energy:

14. Mechanical Energy is a combination of two fundamental types of energy:
Kinetic energy (the energy of motion)
Potential energy (energy that is stored) - Gravitational Potential energy

15. Kinetic Energy
The kinetic energy of an object of mass m, in kg, and speed v, in m/s:
Pg. 226 #3
Pg. 242 #

16. Kinetic Energy The work done by the net force causes a change in speed
The kinetic energy of an object of mass m, in kg, and speed v, in m/s:
Pg. 226 #3
Pg. 242 #

17. Gravitational Potential Energy
Ex: A mass m is lifted from a height h1 to a height h2 at a constant speed.
Derive Gravitational Potential Energy:
- A mass m is lifted from a height h1 to a height h2 at a constant speed. What is the work done? Where did this energy go if it did not speed up?

18. Gravitational Potential Energy
“stored energy” in an object at a particular height w.r.t. a reference point.
Ex: A mass m is lifted from a height h1 to a height h2 at a constant speed.
Derive Gravitational Potential Energy:
- A mass m is lifted from a height h1 to a height h2 at a constant speed. What is the work done? Where did this energy go if it did not speed up?

19. Gravitational Potential Energy
The gravitational potential energy Eg of an object of mass m, in kg, that is at height h, in m, above the reference point is:
g = 9.8 m/s2

20. Gravitational Potential Energy
The gravitational potential energy Eg of an object of mass m, in kg, that is at height h, in m, above the reference point is:
g = 9.8 m/s2

21. W.E.T. (Work-Energy Theorem)
The total work done on an object equals the change in the object’s kinetic energy OR gravitational potential energy, but NOT BOTH.

22. Ex 1: What happens to the kinetic energy of an object when work is done on it?

23. Ex 2: Calculate the work done to speed up a 1500 kg Honda Civic:
From rest to 20 km/h b) From 80 km/h to 100 km/h

24. Ex 3: What role does gravitational potential energy play in the production of electricity by Ontario Power Generation?

25. Ex 4: Ontario Power Generation at Niagara Falls operates under a normal head of about 55 m (height from which water falls). If about 4.54x108 kg of water falls every minute, how many mega-joules of energy are created by the falling water in a hour?