1. Energy

2. What is energy?
In science, energy is defined as the ability to do work.
Work is done when a force makes and object move in the direction of the force applied.
The tennis player does work and transfers energy to the racket. With this energy, the racket can then do work on the ball.

3. Law of Conservation of Energy
Energy cannot be created or destroyed. Energy is transferred.

4. Kinetic and Potential Energy
Kinetic energy is the energy of the motion.
Kinetic energy= mv2/ 2
Kinetic energy is large if the object has a large mass or if it is moving fast.

5. Gravitational Potential Energy is the energy an object has because of its position.
Gravitational potential energy depends on the object’s weight its distance from the ground.
Gravitational pontential energy = weight x height

6. Other types of Energy
Thermal Energy is the kinetic energy from the movement of the particles in an object.
Chemical Energy is the energy stored in chemical bonds that hold compounds together.
Electrical Energy is the energy of moving particles called electrons.
Sound Energy is energy from a vibrating object.
Light Energy is energy from the vibration of electrically charged particles.
Nuclear Energy is the energy stored in the nucleus of an atom.
Fission: two nuclei join
Fusion: large nucleus splits

7. Wasted and Useful Energy
Sankey Diagram

8. Useful energy transfer
Many everyday objects are designed to transfer energy from one form into another useful form.
What energy transfer is an electric fan designed to carry out?
electrical
energy
kinetic
energy

9. What is the useful energy transfer?
What energy transfer is a speaker designed to carry out?
electrical
energy
sound
energy

10. What is the useful energy transfer?
What energy transfer is a wind farm designed to carry out?
Acknowledgement
© Energy Northwest/DOE/NREL
Turbine installation at the Nine Canyon Wind Project; largest wind farm to be built in Washington State.
kinetic
energy
electrical
energy

11. What is the useful energy transfer?
What energy transfer is a hydroelectric power station designed to carry out?
Gravitational potential
energy
electrical
energy

12. Useful energy transfers
Complete the input and useful output energies for the devices in this table.
Device
Input
energy
Output energy
kettle
solar cell
catapult
coal fire
electrical
heat
light
electrical
elastic
kinetic
chemical
heat

13. Wasted energy
Whenever energy is changed from one form to another, some energy is always wasted.
Energy is usually wasted as:
heat energy;
sound energy.
All electrical devices produce a small amount of heat energy, which is normally wasted.

14. car engine hairdryer jet engine washing machine
Wasted sound energy
If you can hear a device that is not designed to make noise then energy is wasted as sound.
Examples of devices that waste energy as sound include:
car engine
hairdryer
jet engine
washing machine

15. car engine television mobile phone charger radio
Wasted heat energy
If a device gets warm and it is not designed to get warm then energy is wasted as heat.
Examples of devices that waste energy as heat include:
car engine
television
mobile phone charger
radio

16. Law of conservation of energy
All energy transfers follow the law of conservation of energy:
Energy cannot be created or destroyed,
just changed in form.
This means that energy never just ‘disappears’.
The total amount of energy always stays the same,
i.e. the total input energy = total output energy.
In most energy transfers, the energy is transferred to several different forms, which may be useful or not useful.
The energy that is transferred to unwanted forms of energy is wasted.

17. Energy transfer in a television
An energy transfer diagram shows the input energy and the output energies for a device. This includes all the useful and wasted forms of energy.
For example, in a television:
light
electrical
sound
heat

18. Energy transfer in a radio
What are the main energy transfers in a radio?
(Don’t forget the wasted energy.)
sound
electrical
heat

19. Energy transfer in a car engine
What are the main energy transfers in a car engine?
(Don’t forget the wasted energy.)
kinetic
chemical
sound
heat

20. Energy efficiency
Efficiency is a measure of how good a device is at changing energy from one form to another.
All devices waste energy, so the efficiency of a device is never 100%.
The more efficient a device
is the less energy is wasted.
Energy efficient light bulbs are more efficient than normal light bulbs because they w____ less energy. More of the e_______ energy that they are supplied with is converted into l____ energy and not h___.
aste
lectrical
ight
eat

21. Calculating efficiency
The efficiency of a device can be calculated using this formula:
efficiency =
useful energy out
total energy in
Useful energy is measured in joules (J).
Total energy is measured in joules (J).
This means that efficiency does not have any units.
It is a number between 0 and 1 or a percentage.

22. Efficiency

23. Efficiency of a bulb
This filament bulb is supplied with 100 J of electrical energy which it converts to 45 J of light energy.
Wasted energy = Total – Useful
= 100 J – 45 J
= 55 J
How much energy
is wasted?
In what form is the energy wasted?
What is the efficiency
of the bulb?
55 J
heat
Efficiency = Useful
Total
= 45 J
100 J
= 0.45 or 45%
0.45 or 45%

24. Efficiency of a radio
This radio is supplied with 300J of electrical energy which it converts to 96J of sound energy.
Wasted energy = Total – Useful
= 300 J – 96 J
= 204 J
How much energy
is wasted?
In what form is the energy wasted?
What is the efficiency of the radio?
204 J
heat
Efficiency = Useful
Total
= 96 J
300J
= 0.32 or 32%
0.32 or 32%

25. Efficiency of a television
This television converts
2 000J of electrical energy into useful energy at an efficiency of 65%.
What useful energy does a television produce?
How much useful
energy is produced?
light and sound
Efficiency = Useful
Total
Useful = Efficiency x Total
= 0.65 x J
= J
1 300 J

26. Sankey Diagram
Sankey diagram is used for expresing the transference of one form of energy into one or more forms.
Draw a Sankey diagram with each of the problems you have solved.