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Chapter 37 Work,
Power & Energy
The word energy comes from the Greek
word energeia
Objectives
In this section, you will learn:
The definition of work and its units, how to calculate
work done.
Definition of power, its units and how to do
calculations involving power.
The definitions and units of energy.
The different forms of energy.
The principle of the conservation of energy.
The sources of energy.
About renewable and non-renewable energy sources.
Conservation of energy
Energy conversions and experiments to demonstrate
Methods of saving energy
What is energy?
work or
Energy is the ability to do _______
move something.
Work is done when a force moves an object.
Work done = force x distance
A body that has energy is able to do work.
Energy is measured in Joules.
For example, a person needs 1000 Joules
of energy to walk up the stairs.
We get this energy from respiration
(i.e. using oxygen to release energy
from food).
Joule
James Prescott Joule (1818-1899) was an English
brewer whose hobby was physics. His name was given
to a unit of energy, the joule, and to a law showing
how much heat is developed by a given electric current
.
in a circuit
There are many different forms of energy.
Can you name some?
Forms of Energy
Energy can exist in many different forms:
Two main groups:
A. Stored energy
B. Energy in action
A. Stored Energy
1. Potential Energy = stored energy.
Example: the stored energy that
water has behind a dam or energy
stored in stretched elastic bands.
2. Kinetic Energy – energy in moving objects.
e.g. a car travelling along a road has kinetic energy.
3. Nuclear Energy
The nucleus at the centre of an atom has
an enormous supply of stored energy.
Nuclear energy is released in nuclear
reactors and nuclear bombs
4. Chemical Energy
Coal
Oil
Battery
Food
Chemical Energy is stored in oil, gas or other fuels. It
is also stored in food.
B. Energy in Action
1. Kinetic Energy = Energy
associated with all moving
objects
2. Heat Energy
The hotter the water particles in a boiling
kettle the faster they move around
3. Light Energy
Light Energy travels in waves and is an important
source of energy for our planet.
4. Sound Energy
Sound Energy is caused by vibrations.
Electrical Energy
Electrical energy comes from moving charges. It is
easily changed to other forms of energy e.g.
electrical energy to light energy in a lamp
Magnetic Energy
Magnetic energy is the ability of certain
substances to attract or repel other
substances
Now, in your copy write down all the different forms
of energy that you can remember…….
Review Questions
1. Energy is the ability to do___________.
HINT
2. What unit is energy measured in?
HINT
Question to think about!
Can energy be destroyed?
Conserving Energy
Energy is expensive to make and some sources are
limited.
It makes sense to conserve energy by:
Insulating buildings.
Turning off energy sources, e.g. lights and electronic
equipment, when not needed.
Recycling materials.
Principle of Conservation of Energy
States that:
Energy is neither created nor destroyed but can be
converted from one form to another.
Energy comes in many forms and can be converted from
one form to another.
Example of Conservation of Energy
In a light bulb only 5% of electrical energy
appears as light.
The remaining energy is turned into heat
energy. The heat energy is lost by the light
bulb.
1.
2.
3.
4.
5.
Review
What is Energy?
Name two types of stored energy?
Name two types of energy in action?
What word is used to describe the energy
associated with moving objects?
What is the principle of conservation of
energy?
Answers:
1. What is Energy?
Energy is the ability to do work or move
something.
2. Name two types of stored energy?
Potential energy, chemical energy, nuclear
energy
3. Name two types of energy in action?
Kinetic energy, heat energy, light energy,
sound energy, electrical energy, magnetic
energy
Answers:
4. What word is used to describe the energy
associated with moving objects? Kinetic
energy
5. What is the principle of conservation of
energy? Energy cannot be created or
destroyed but it can change from one
form to another.
Objectives of lesson
1. Investigate some sources of energy on the
planet
2. Discuss Ireland’s energy needs
3. Investigate which energy source is best to
use
4. Consider ways to conserve energy in our
home and school.
5. Carry out an experiment to show
chemical energy changing to electrical
energy to heat energy
Sources of Energy
1. The Sun
Primary source of energy on planet
a) Green plants need the sun for photosynthesis.
b) Heat from the sun keeps us warm
Solar panels and solar cells can trap the suns
energy and turn it to heat and electricity
2. Fossil Fuels
Remains of dead plants and animals get
squashed and these turn into peat, coal, oil and
gas. These substances are called fossil fuels.
In Ireland we mainly use peat, gas,
coal and oil to make electricity.
Fossil Fuels
Fossil Fuels are nonrenewable sources of
energy
3. Renewable Energy Sources
Renewable sources of energy are those that
will never be used up.
•Usually does not produce harmful waste
products (exception nuclear energy).
•Expensive to set up.
Renewable and non-renewable energy sources
Renewable sources will last almost forever,
non-renewable sources will run out.
Non-renewable
sources
Renewable sources
Oil
Wind
Coal
Solar
Gas
Nuclear
Turf
Biomass and
geothermal
Even with renewable sources, there can be
disadvantages, such as the dangerous waste
of nuclear energy.
4. Nuclear Energy
Nuclear energy is released by splitting up a
large nucleus into two parts in a nuclear
reactor.
1kg of uranium can produce as much energy
as 3,000,000kg of coal.
Nuclear Energy
No nuclear energy in Ireland
Closest nuclear plant is in
Sellafield in the UK
Problems with Nuclear Energy
Radioactive substances are produced by
splitting the atom. Disposal of these
substances is dangerous and expensive
Radiation can damage living cells and cause
cancers.
Nuclear Fusion
Nuclear fusion is another method of
producing energy from a nucleus.
Light nuclei are forced to join together
producing a fuel called deuterium which is a
form of hydrogen.
The advantages would be a cheap, clean and
endless supply of fuel
5. Other Sources of Energy
Hydrogen
Fuel cells which turn hydrogen into
electricity are used in things like space
travel.
Energy Sources
Advantages and Disadvantages
See text book pg 295-298
Select two energy sources and write out their
original source, one advantage and one
disadvantage
Which Energy Source is best?
Different sources of energy suit different
areas in the world
e.g. In hot countries solar power stations are
worth building
Conserving Energy
Make a list of 3 ways you could conserve
energy in your home
Conserving Energy in your home
1. Put lagging jackets on hot water tanks
2. Insulate attics with polystyrene or fibre
glass
3. Double glaze windows
Energy Conversions
Some examples of energy conversions:
In a battery:
Chemical energy→electrical energy→light energy and
heat energy
In a solar panel connected to a fan:
Light energy→electrical energy→kinetic energy
Mandatory Experiment
a) To show chemical energy changing to
electrical energy to heat energy t/b pg. 299
Apparatus: Battery, beaker, coil of nicrome
wire, connecting wires, cold water,
temperature sensor and data logging
equipment
Safety:
Method:
1.Place the resistant wire under the cold
water in the beaker
2. Connect the resistance wire to the battery as shown in
the diagram.
3. Place the temperature sensor in the cold water and
note the temperature after a few minutes.
4. Turn on the switch and note the temperature of the
water every 2 minutes using the temperature sensor.
5. Record your results.
What is the energy conversion shown in this
experiment?
Result of experiment:
Energy Conversion:
Chemical Energy -> Electrical Energy -> Heat Energy
Result:
The temperature of the water rises as long as the battery is
supplying energy.
Conclusion:
The chemical energy of the battery was changed to electrical
energy in the circuit. The electrical energy in the resistant wire
was changed to heat energy and this heat energy raised the
temperature of the water
Experiment:
To show electrical energy changing to magnetic energy
to kinetic energy p.g. 300
Apparatus: long nail, length of insulated wire, power
supply, paper clips
Safety:
Method:
1.Wind the insulated wire closely around the nail
2.Connect the two ends of the wire to a power supply
3.Place some loose paper clips under the nail.
4.Switch on the current and see what happens
5.Switch off the current and notice what happens
Result:
Energy Conversion:
Conclusion:
Result: When the current flows the paper clips are attracted to
the nail and insulated wire. When the current is switched off
the paperclips are not attracted to the nail and insulated wire.
Energy Conversion:
Electrical energy -> magnetic energy -> kinetic energy
Conclusion:
The electrical energy from the power supply changes to
magnetic energy in the nail. The magnetic energy in the nail
causes the paper clips to move towards the nail. (The kinetic
energy of the paperclips is changed to potential energy)
Experiment: To show light energy changing to
electric energy to kinetic energy
Apparatus: solar cell, electric motor, light source e.g.
lamp, connecting wires.
Safety:
Method:
1.Connect the solar cell to a miniature electric motor
2.Place the solar cell in the path of light from a lamp and
note what happens
3.Block the light shining on the solar cell and note what
happens
Result:
Result:
When the light from the lamp shines on the solar cell it
makes the fan on the solar cell move. When no light
shines on the solar cell the fan stops moving.
Energy Conversion:
Conclusion:
Energy Conversion:
Electrical energy -> light energy -> electrical energy -> kinetic
energy
Conclusion:
Electrical energy is changed to light energy in the lamp and
then to electrical energy in the solar cell. The electrical energy
is changed to kinetic energy when the fan moves on the solar
cell.
Review of Energy (Fill in the blanks)
1.
2.
3.
Energy is the ________________________________________
The unit of energy is J_________
The Principle of Conservation of Energy states that_________
can neither be _________ or _________ but can from one form
to another
4.
Types of stored energy include: P____________, C _________
and nuclear energy
5. Types of energy in action include: K___________, H_________ and
L____________
6. Potential Energy is ___________________________________
7. Kinetic Energy is ________________________________________
8. Name two renewable sources of energy?
9. Name two non-renewable sources of energy?
10. List two ways you can conserve energy at home?
11. List two ways you can conserve energy in school?