1. Energy & Its Impact on Global Society
Jerome K. Williams, Ph.D.
Saint Leo University
Dept. Mathematics & Sciences

2. Chapter 2: Energy Mechanics
Energy & Work
Heat
First Law Thermodynamics
Examples of Work & Energy
Power & Electrical Applications

3. Energy & Work Energy is the “capacity to do work.”
Work is the product of a force in the direction of motion times the object’s displacement.
W = F x d

4. Motion

5. Energy & Work Units (Energy & Work) Table 2.4 (Units in Mechanics)
SI System: Newton x meters = Joules (J)
English System: Foot-pounds = ft-lb
Table 2.4 (Units in Mechanics)

6. Energy & Work Work is one way of transferring energy to an object
W = Δ(KE + PE)
Thermal Energy (TE) of object is a function of its temperature

7. Energy & Work
Thermal Energy (TE) of object is a function of its temperature; it is equal to total of all the microscopic energies of the molecules that comprise an object.
W = Δ(KE + PE + TE)

8. Heat
Addition of heat is another way of transferring energy to a system
Heat is the energy transferred as a result of a temperature difference between two objects.
W = Δ(KE + PE + TE)

9. First Law of Thermodynamics
Thermal energy of an object can be changed by doing work (W) as well as adding heat (Q).
First Law of Thermodynamics: total energy of a system can be increased by doing work on it or by adding heat.
W + Q = Δ(KE + PE + TE)

10. The First Law: Equations & Math
PEG = weight x height = mgh
g = acceleration due to gravity g = 9.8 m/s2

11. Examples of Work & Energy
A man pushes a box across the floor by exerting a force of 150 N on it in the direction of motion. If the box moved 3 m, how much work (W) did he do?
Answer 450 J

12. Examples of Work & Energy
What is the kinetic energy of a 80 kg person walking with a speed of 1 m/sec?
Answer 40 J

13. Examples of Work & Energy
What is the potential energy does a 50 kg person standing on the roof of a house 4 m off the ground?
Answer J

14. Power & Electrical Applications
Another basic concept of energy mechanics is power.
Power is the rate of doing work or the rate at which energy is used, produced, or transferred.

15. Power & Electrical Applications

16. Power & Electrical Applications
Units for Power are energy divided by time
Watt is SI unit for power (1 Watt = 1 Joule/sec)
More common unit is kilowatt (kW) which is the same as 1000 Watts.

17. Power & Electrical Applications
Units for Power are energy divided by time
English system uses ft-lb/sec as unit for power
Another common unit is horsepower (hp)
1 hp = 746 Watts and 1 hp = 550 ft-lb/sec

18. Power & Electrical Applications
Average power expended per person per year in US is around 12 kW
In most countries, higher standards of living (measured by GDP per capita) are matched by higher levels of energy consumption per capita

19. Power & Electrical Applications
Rate of producing electricity is electrical power measured in watts.
A modern-size power plant produces electrical energy in billions of watts or 1000 megawatts (1000 MWe) where e signifies electrical power output

20. Power & Electrical Applications
Many power plants in US still rely on coal to operate; however, newer plants are relying on renewable energy sources
Hydropower plants provide about 10% of US total electrical energy needs

21. Power & Electrical Applications
If it takes 2 seconds to raise an 8 kg block a vertical height of 1 m, what is the power expended?
Answer 39 W

22. Power & Electrical Applications
Ascending to the top of Muir Pass in the Sierra Nevada Mountains in California, Robert climbed 2000 feet (vertically) in a time of 2.5 hours. What was his average power expended (in watts)? Robert plus his backpack weigh 180 lb.
Answer 54 W

23. Power & Electrical Applications
An electric heater has a power rating of 1500 watts (1.5 kW). If the heater is run for 6 hours, and electricity costs $.12 per kWh, how much will it cost to run the heater for this time interval?
Answer $1.08

24. Suggested Problems
3, 4, 16, 19, 27, 30, 32