3. Section 1: What is Energy?
By the end of this section, you should be able to:
o Explain the relationship between energy and work.
o Compare kinetic energy and potential energy.
o Describe the different forms of energy.
4. Energy & Work: Working Together
o Energy is the ability to do work.
o Work is done when a force causes an object to
move in the direction of the force. Work is a transfer
of energy.
o Energy and work are expressed in units of joules
(J).
6. Kinetic Energy
o Kinetic energy is the energy of motion. All moving
objects have kinetic energy.
o The amount of kinetic energy that an object has
depends on its mass and velocity.
9. Potential Energy
o Potential energy is the energy an object has
because of its position.
o The amount of gravitational potential energy that an
object has depends on its weight and its height.
12. Potential Energy
o When you find out an object’s gravitational potential
energy, the “ground” that you measure the object’s
height from depends on where it is.
o The height you use in calculating gravitational
potential energy is a measure of how far an object
has to fall.
13. Mechanical Energy
o Mechanical energy is the total energy of motion and
position of an object. Both kinetic energy and
potential energy are kinds of mechanical energy.
Mechanical Energy [ME] = Potential Energy [PE] + Kinetic Energy [KE]
14. Mechanical Energy
o The mechanical energy of an object remains the
same unless it transfers some energy to another
object.
o But even if the mechanical energy of an object stays
the same, the potential energy or kinetic energy can
increase or decrease.
15. Other Forms of Energy
o Thermal energy is all of the kinetic energy due to
random motion of the particles that make up an
object.
o All matter is made up of particles that are always in
random motion. So, all matter has thermal energy.
16. Other Forms of Energy
o Thermal energy increases as temperature increases
and increases as the number of particles increases.
17. Other Forms of Energy
o Chemical energy is the energy of a chemical
compound that changes as its atoms are
rearranged.
o Chemical energy is a form of potential energy
because it depends on the position and
arrangement of the atoms in a compound. The
energy in food is chemical energy.
18. Other Forms of Energy
o Electrical energy is the energy of moving electrons.
Electrical energy can be thought of as potential
energy that is used when you plug in an electrical
appliance and use it.
19. Other Forms of Energy
o Sound energy is caused by an object’s vibrations.
The object’s vibrations transmit some kinetic energy
to the air particles, which also vibrate. These
vibrations transmit sound energy.
20. Other Forms of Energy
o Light energy is produced by the vibrations of
electrically charged particles.
21. Other Forms of Energy
o Nuclear energy is energy that comes from changes
in the nucleus of an atom. Nuclear energy can be
produced when nuclei are joined in a fusion reaction
or when a nucleus is split apart in a fission reaction.
23. Warmup
What do the following have in common: a plant, a
Bunsen burner, and a pendulum?
24. Section 2: Energy Conversions
By the end of this section, you should be able to:
o Describe an energy conversion.
o Give examples of energy conversions for the
different forms of energy.
o Explain how energy conversions make energy
useful.
o Explain the role of machines in energy conversions.
25. Kinetic and Potential Energies
o An energy conversion is a change from one form of
energy to another. Any form of energy can change
into any other form of energy.
o As a skateboarder travels up and down the halfpipe, his energy changes back and forth between
kinetic energy and potential energy.
27. Kinetic and Potential Energies
o Stretching a rubber band stores elastic potential
energy in the rubber band.
o When you let the rubber band go, it goes back to its
original shape. It releases its stored-up potential
energy as it does so.
28. Conversions Involving Chemical Energy
o Chemical energy is stored in the food you eat. Your
body uses this chemical energy to function.
o The chemical energy in the food you eat comes
from the sun’s energy.
29. Conversions Involving Chemical Energy
o Plants, through the process of photosynthesis,
change light energy into chemical energy.
30. Conversions Involving Chemical Energy
o The chemical energy in the food you eat is changed
into another kind of chemical energy that your body
can use.
o Your body then uses that energy to give you kinetic
energy that you use in everything you do.
31. Why Energy Conversions are Important
o Energy conversions are needed for everything we
do. Heating our homes, getting energy from a meal,
and many other things use energy conversions.
o Machines, such as a hair dryer, help harness energy
and make that energy work for you.
32. Why Energy Conversions are Important
o Some common energy conversions that involve
electrical energy are shown in the table below.
Alarm clock
Electrical energy light and sound energy
Battery
Chemical energy electrical energy
Light bulb
Electrical energy light and thermal energy
Blender
Electrical energy kinetic and sound energy
33. Energy and Machines
o A machine can make work easier by changing the
size, direction, or both of the force needed to do the
work. Some machines allow you to use less force
over a greater distance to do the same amount of
work.
o Some machines help you use energy by converting
it into the form that you need.
36. Warmup
o Where does the energy that makes a roller coaster
car move come from?
o Where does the energy go?
37. Section 3: Conservation of Energy
By the end of this section, you should be able to:
o Explain how energy is conserved within a closed
system.
o Explain the law of conservation of energy.
o Give examples of how thermal energy is always a
result of energy conversion.
o Explain why perpetual motion is impossible.
38. Where Does the Energy Go?
o Friction is a force that opposes motion between two
surfaces that are touching.
o For a roller coaster car to move, energy must be
used to overcome friction between the car’s wheels
and the track.
o As a result, not all of the car’s potential energy
changes into kinetic energy and not all of the car’s
kinetic energy changes back into potential energy.
39.
40. Energy is Conserved Within a Closed System
o A closed system is a group of objects that transfer
energy only to each other
o The Law of Conservation of Energy states that
energy cannot be created or destroyed.
o Energy can be converted from one form to another.
But all of the different forms of energy in a system
always add up to the same total amount of energy.
41. No Conversion Without Thermal Energy
o Any time one form of energy is converted into
another form, some of the original energy always
gets converted into thermal energy.
o The thermal energy due to friction that results from
energy conversions is not usually useful energy.
42. No Conversion Without Thermal Energy
o A perpetual motion machine is a machine that would
run forever without any additional energy.
o But perpetual motion machines are impossible
because some waste thermal energy always results
from energy conversions.
43. No Conversion Without Thermal Energy
o Some systems transform energy with less loss of
heat than others do. Such systems are more
efficient than others are.
o Improving the efficiency of machines is important
because greater efficiency results in less waste. If
less energy is wasted, less energy is needed to
operate a machine.
45. Warmup
Predict whether the following sources of energy
are renewable or nonrenewable.
sunlight
petroleum
coal
nuclear
wind
geothermal
46. Section 4: Energy Resources
By the end of this section, you should be able to:
o Name several energy resources.
o Explain how the sun is the source of most energy on
Earth.
o Evaluate the advantages and disadvantages of
using various energy resources.
47. Nonrenewable Resources
o Nonrenewable resources cannot be replaced or are
replaced much more slowly than they are used.
o Fossil fuels are nonrenewable energy resources that
formed from the remains of organisms that lived
long ago. Oil, natural gas, and coal are the most
common fossil fuels.
48.
49. Nonrenewable Resources
o All fossil fuels contain stored energy from the sun,
which can be converted into other kinds of energy.
o Burning coal is a common way to generate electrical
energy. Petroleum is used to make gasoline, wax,
and plastics. Natural gas is often used in home
heating.
50. Nonrenewable Resources
o Electric generators convert the chemical energy in
fossil fuels into electrical energy by the process
shown below.
51. Nonrenewable Resources
o Another way to generate electrical energy is to use
nuclear energy.
o In a process called nuclear fission, the nucleus of a
radioactive atom is split into two smaller nuclei,
which releases nuclear energy.
o Because the supply of radioactive elements is
limited, nuclear energy is a nonrenewable resource.
52. Renewable Resources
o Renewable resources are naturally replaced more
quickly than they are used.
o Sunlight can be changed into electrical energy
through solar cells.
o Solar cells can be used in devices such as
calculators. They can also be placed on the roof of a
house to provide electrical energy.
53. Renewable Resources
o The potential energy of water in a reservoir can be
changed into kinetic energy as the water flows
through a dam.
o In a hydroelectric dam, falling water turns turbines.
The turbines are connected to a generator that
changes kinetic energy into electrical energy.
54. Renewable Resources
o The kinetic energy of wind can turn the blades of a
windmill or a wind turbine.
o A wind turbine changes the kinetic energy of the air
into electrical energy by turning a generator.
55. Renewable Resources
o Geothermal energy is thermal energy caused by the
heating of Earth’s crust. This energy can be
converted into electrical energy at geothermal power
plants.
o Biomass is organic matter, such as plants, wood,
and waste, that can be burned to release energy.
Some countries depend on biomass for energy.
56. The Two Sides to Energy Resources
o All energy resources have advantages and
disadvantages. Many factors determine when one
energy source is a better choice than another.
o Energy planning in all parts of the world requires
careful consideration of energy needs and the
availability and responsible use of resources.
57. The Two Sides to Energy Resources
Take a look at the Table on p.146
