1. Forms and Uses of Energy

2. 16.1 What is Energy? Energy is the ability to do work.
Living things need energy for the processes that keep them alive.
Non-living systems also need energy to function.
For example, cars and aeroplanes need fuel to provide them with energy to move.

3. 16.2 Forms of Energy Potential Energy
Potential energy is stored energy due to a body’s position or condition.

4. 16.2 Forms of Energy Examples of potential energy:
Chemical potential energy
Energy stored in fuels such as petrol and food that can be released through chemical reactions.

5. 16.2 Forms of Energy Examples of potential energy:
Gravitational potential energy
Energy that an object has because of its position or location.
When the object is in a higher position with respect to the ground, it has more gravitational potential energy than in a lower position.

6. 16.2 Forms of Energy Examples of potential energy:
Elastic potential energy
Energy that an object has when it is stretched or compressed.

7. 16.2 Forms of Energy Kinetic Energy
Kinetic energy is the energy that a body has due to its motion.
All moving objects have kinetic energy.
Examples: a bird flying in the sky, a girl walking down the street and a car speeding down the road.

8. 16.2 Forms of Energy
Heat
Heat is the energy that flows from a region of higher temperature to one of lower temperature.
Heat flows from things that are hot.
The Sun is an important source of heat energy during the day.
Heat is used in homes for cooking, heating water, ironing clothes.
In factories, heat is needed for processes like melting metals, creating steam to turn turbines and making chemicals react.

9. 16.2 Forms of Energy Light Light is the energy that enables us to see.
Things that are luminous can give out light energy.
The Sun is an important source of light energy during the day.
Without light, the world would be completely dark, and we would not be able to see things around us.

10. 16.2 Forms of Energy
Sound
Sound is the energy produced when objects vibrate.
Sound allows us to communicate and enjoy music.
Sound is also used as a warning.
For example, when a fire breaks out, the fire alarm goes off and alerts everyone to get to safety.

11. 16.2 Forms of Energy Electricity
Electricity or electrical energy is the energy that results from the flow of charged particles.
Electricity is a useful form of energy that can be transformed into many other forms of energy.
Almost all electrical appliances or equipment in homes and offices need electricity to work.

12. 16.3 Energy Transformations
Photosynthesis in plants
Light energy  Chemical potential energy

13. 16.3 Energy Transformations
An archer releasing his bow
Elastic potential energy  Kinetic energy

14. 16.3 Energy Transformations
A moving car
Chemical potential energy  Kinetic energy + Sound energy + Light energy + Heat energy

15. 16.3 Energy Transformations
Generation of electricity
Electricity is a useful form of energy.
Electrical generators are used to convert kinetic energy to electricity.
Power stations produce large amounts of electricity needed in homes, schools and offices.
In a power station, a series of energy changes occur before electricity is produced.

16. 16.3 Energy Transformations
3. The turbines are connected to a generator, which converts the kinetic energy of the turbine blades into electricity.
Kinetic energy of turbines  Electricity
2. The heat energy turns water into steam at high pressure, which goes through the boiler and turns the turbines.
Potential and kinetic energy of steam  Kinetic energy of turbines
In a power station
1. A fuel such as coal, oil or natural gas is burnt and heat is produced to boil the water in the boiler.
Chemical potential energy of fuel  Heat energy of water
steam line
turbine
generator
coal supply
switchyard
boiler
condenser
cooling water

17. 16.3 Energy Transformations
Generation of electricity
In a nuclear power station, nuclear reactions occur by bombarding radioactive elements with neutrons.
This creates large amounts of heat to boil the water into steam to turn turbines.
Nuclear energy in radioactive elements  Heat  Kinetic energy of steam  Kinetic energy of turbines  Electricity

18. 16.4 Law of Conservation of Energy
Energy transformations in a swing
When the swing is at its highest point, A, it only has gravitational potential energy. When the swing is midway between A and B, some of the gravitational potential energy is converted to kinetic energy.
When the swing is at its lowest point, B, all the gravitational potential energy has been converted to kinetic energy. A C B

19. 16.4 Law of Conservation of Energy
Energy transformations in a swing
In theory, the child would be able to swing to and fro for an unlimited period of time.
However, the swing will eventually stop moving if no one gives it a push every now and then. What happened to the energy?
The law of conservation of energy states that energy can change from one form to another, but it cannot be created or destroyed.
When energy is not lost, we say it is conserved. The swing stops moving as the energy was converted to other forms of energy such as heat and sound energy due to friction between the swing and surrounding air.

20. 16.4 Law of Conservation of Energy
Energy transformations in a ball falling on the floor
Let the total energy possessed by the ball be E.
According to the conservation of energy, the total amount of energy, E, does not change.
At position B, the ball is falling. It gains kinetic energy, KEB, while losing some potential energy. The potential energy left at position B is PEB .
KEB + PEB = PEA = E A
At position A, the ball has potential energy PEA. This is equal to E.
PEA = E B
At D, the ball hits the floor and becomes compressed. A sound is heard and heat is produced due to friction.
Elastic potential energy of ball + heat + sound = E
At position C, just before the ball hits the floor, only kinetic energy KEC is left.
KEC = PEC + KEC = PEA = E C D

21. 16.4 Law of Conservation of Energy
Energy transformations in a ball falling on the floor
Then ball is unable to reach its original height of position A when it bounces back up.
This is because some of the energy, E, is lost as sound and heat when it hits the floor.
With less energy, the ball cannot regain its original height. A B C D

22. 16.5 Conserving Energy
It is important to conserve energy because most of the energy we use comes from non-renewable resources.
Non-renewable resources include crude oil and coal. These sources of energy are limited and will run out one day.
Coal power plants produce more pollution than oil power plants. But coal is more commonly used in developing countries as it is cheaper than oil.
Extracting, processing and burning crude oil cause large amounts of pollution, which destroy the environment.

23. Renewable sources of energy
Renewable sources of energy are sources of energy that can be sustained or renewed indefinitely, due to unlimited supplies or because of new growth.

24. Renewable sources of energy
Solar energy
Solar energy is used in solar furnaces for smelting iron.
Solar energy is also used to generate steam in power station. This steam is used to turn turbines of a generator to produce electricity.

25. Renewable sources of energy
Wind energy
A wind farm is a collection of wind turbines used to generate electricity.
The wind turbines use the kinetic energy of the wind to generate electrical energy.

26. Renewable sources of energy
Wave energy
Wave farms use the kinetic energy of waves to generate electricity.
The up-and-down movement of the wave will shift gears to turn turbines to generate electricity.

27. Renewable sources of energy
Biomass
Biomass refers to plant and animal material from which we can:
extract oil (oil palm, jatropha, jojoba)
ferment into gas (water hyacinth, manure)
burn (dried plant material, wood, charcoal)

28. Renewable sources of energy
Conserving energy in Singapore
Singapore uses natural gas for its power stations but has started using solar energy, wind energy and biomass.
Since Singapore does not have many natural resources, we are dependent on other countries for our fuel needs.
Hence, it is important for us to be aware of conserving energy.

29. Renewable sources of energy
Conserving energy in Singapore
We should use energy more efficiently and avoid wasting electricity.
For example, you should turn off electrical appliances that are not in use.

30. Miscellaneous