1. Pearson Prentice Hall Physical Science: Concepts in Action
Chapter 15
Energy

2. 15.1 Energy and Its Forms Objectives:
1. Describe and compare how energy and work are related
2. Explain what factors kinetic energy of an object depends on
3. Discuss how gravitational potential energy is determined
4. Summarize the major forms of energy

3. How Energy & Work are Related + Kinetic Energy
Def: energy is the ability to do work
Work is a transfer of energy
Def: kinetic energy is the energy of motion
The kinetic energy of any moving object depends on its mass and speed
The formula is: KE = ½ mv2 where m = mass and v is the velocity (which must be squared)
the units for m are kg & v = (m/s)2 or m2/s2
the units for PE are kg*m2/s2 which is also called joules, J

4. Potential Energy
Def: potential energy is stored energy as a result of position or shape
PE is energy with the potential to do work
Two forms of PE are gravitational PE and elastic PE
Def: gravitational PE is PE that depends upon an object’s height
Gravitational PE increases when an object is at a higher height

5. An object’s gravitational PE depends on its mass, height & acceleration due to gravity
The formula for gravitational PE = mgh where m= mass (kg), g= 9.8 m/s2 (the free fall acceleration of gravity) & h = height in meters, m
When you multiply all the units together you get kg*9.8m/s2*m or kg*m2/s2 which is J
Def: elastic PE is the PE of an object that is stretched or compressed
An object is elastic if it springs back after being stretched

6. Practice Problems Calculate the KE of a 1500kg car moving at 29m/s.
A bowling ball traveling at 2.0m/s has 16J of KE. What is the mass of the bowling ball in kg?

7. Practice Problems
Calculate the PE of a car with a mass of 1200kg at the top of a 42m hill.
Calculate the PE of a 55g egg held out of a 2nd story window, 6m off the ground.

8. Forms of Energy
The major forms of energy are mechanical energy, thermal energy, chemical energy, electrical energy, electromagnetic energy and nuclear energy
Def: mechanical energy is the energy associated with the motion and position of everyday objects
Def: thermal energy is the total PE and KE of all the microscopic particles in an object

9. Def: chemical energy is the energy stored in chemical bonds
Def: electrical energy is the energy associated with electric charges
Def: electromagnetic energy is a form of energy that travels through space in the form of waves
Def: nuclear energy is the energy stored in atomic nuclei

10. 15.2 Energy Conversion & Conservation
Objectives:
1. Describe how energy can be converted from one form to another
2. Explain the law of conservation of energy
3. Discuss the energy conversion that takes place as an object falls toward Earth
4. Discuss how energy and mass are related

11. Energy Can be Converted from One Form to Another
Def: energy conversion is the process of changing energy from one form to another
Sometimes energy is converted to other forms in a series of steps
Ex: striking a match uses chemical energy from your muscles, then friction between match and box converts KE to thermal energy, thermal energy triggers a chemical reaction releasing more chemical energy
Often energy converts directly from one form to another
a wind up toy, for example, is PE to KE

12. Conservation of Energy + Energy Conversions and Gravity
The Law of Conservation of Energy states that energy cannot be created or destroyed
The gravitational PE of an object is converted to the KE of motion as an object falls
Pendulums constantly convert PE to KE and KE to PE as the pendulum swings
At the bottom of the swing, the pendulum has maximum KE and zero PE
On either side the pendulum will have a combination of PE + KE
Q: Where is the PE the greatest and KE zero?

13. Energy and Mass Mechanical energy = KE + PE
Mechanical energy is also conserved
(KE + PE)beginning = (KE + PE) end
Einstein has an equation: E = mc2 where E is energy (J), m is mass (kg) & c2 is the speed of light squared (3 x 108 m/s)2
This equation says that energy and mass are equivalent and can be converted into each other
It also means that a tiny amount of matter can produce enormous amounts of energy
Mass and energy together are always conserved

14. 2. Explain how energy resources can be conserved
Objectives:
1. Give examples of the major nonrenewable and renewable energy sources
2. Explain how energy resources can be conserved

15. Nonrenewable and Renewable
Nonrenewable energy resources include oil, natural gas, coal and uranium
Oil, natural gas and coal are fossil fuels
Fossil fuels were formed underground from once living organisms
Most nonrenewable resources are considered inexpensive, available and are known to cause pollution

16. Renewable energy resources include hydroelectric, solar, geothermal, wind, and biomass
Def: hydroelectric energy is energy obtained from flowing water
Hydroelectric energy production usually involves the building of a dam
Hydroelectric is available, used today and generally nonpolluting
Def: solar energy is sunlight converted to usable energy
Solar energy is expensive and its use is limited until technology improves

17. Def: geothermal energy is thermal energy beneath the earth’s surface
It is nonpolluting and available in this area due to naturally occurring hot springs
most places are not near a volcano or hot springs
Def: biomass energy is the energy stored in living things
Biomass can be converted directly to thermal energy
Agricultural waste such as turning corn into ethanol for auto fuel is an example
This technology is moderately expensive

18. Wind energy requires a lot of land and a place that has a lot of wind
It is expensive and not practical at this time although research continues
Hydrogen fuel cells are being used in some places to generate electricity by reacting hydrogen with oxygen
The main source of hydrogen is water
This technology is expensive and considered to be a research and development project for future energy sources

19. Conservation of Resources
Energy resources can be conserved by reducing energy needs and by increasing the efficiency of energy use
Def: energy conservation is finding ways to use less energy or use energy more efficiently
Q: Can you think of some ways we can conserve energy resources?