Pearson Prentice Hall Physical Science: Concepts in Action

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. 15.3 Energy Resources • 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?