The Various Forms and Sources of Energy



1. Things have energy if they can do work. Energy is the ability to do work.


2. The unit of energy is joule (J).


3. All living things need energy to do work. Energy makes things grow, keeps us warm and sustains life. Without energy, all living things would not survive.


4. Energy is also needed for machined to do our work. Without energy supplies, all our machines would stop working and we would be able to do very little work.


Various Forms of Energy

1. Energy can exist in many different forms as shown in Figure 6.1.


2. Working energy is the form of energy that involves work being done. The effects of energy changes can be seen.


3. Stored energy is the form of energy which is less obvious. It is stored and can be released by a conversion process.


Kinetic Energy

1. Kinetic energy is the energy of an object due to its motion.


2. All moving objects possess kinetic energy.


3. The faster an object moves, the greater is its kinetic energy.


4. All stationary (not moving) objects have zero kinetic energy.


Potential Energy

1. Potential energy is the energy stored by an object due to its position or its condition.


2. All objects above the ground have gravitational potential energy because of their raised position.


3. The gravitational potential energy of an object depends on

    (i) the mass of the object,

   (ii) the height or position of the object above the ground, and

  (iii) the strength of the gravitational pull on the object.


4. The bigger the mass, the greater the potential energy.


5. The higher the position of an object from the ground, the more potential energy it has.


6. Potential energy is also stored in objects which are compressed, stretched or bent.


7. All elastic substances when stretched or compressed possess elastic potential energy because of their stretched or compressed condition.


Chemical Energy

1. Chemical energy is the energy stored in substances such as food and fuels.


2. The stored chemical energy is released and converted to other forms of energy when the substances undergo chemical reactions.


Sound Energy

1. Sound energy is produced by vibrating objects.


2. Sound energy can be transferred from one place to another in the form of waves through a medium such as air, water or solid.


3. Sound energy cannot pass through a vacuum as there are no molecules in a vacuum to transfer the energy.


Heat Energy

1. Heat energy is the energy found in hot objects.


2. The hotter the object, the more energy it can give out.


3. Heat energy can increase the temperature of an object.


4. Heat energy is also known as thermal energy. The heat energy that is stored in a hot body depends on its temperature and volume. The higher the temperature, the higher the amount of heat energy that can be stored in the body.


5. The Sun is our main source of heat energy.


Light Energy

1. Light energy is the energy radiated (spread out) by luminous objects (objects that give out light).


2. Light energy enables us to see things around us.


Electrical Energy

1. Electrical energy consists of electric charges, which travel through electrical conductors or wires.


2. Electrical energy is supplied in the form of electrical power by generators, batteries, dry cells and solar cells.


3. Electrical energy is widely used because it can be easily generated, transported and changed to other forms of energy.


Nuclear Energy

1. Nuclear energy is the energy stored in the nucleus of an atom.


2. All radioactive materials store nuclear energy. When radioactive materials decay, energy is released because of the changes in the nuclei of the atoms.


3. Nuclear energy is also released when a particle penetrates a large nucleus and causes it to split into many smaller nuclei. This process is called nuclear reaction.


4. A nuclear reactor is used to control the nuclear reaction and the energy released. The nuclear energy is then converted to heat energy and the steam produced is used to generate electricity in a power station.


5. The nuclear energy generated from a nuclear reactor also provides direct mechanical power to operate a ship or a submarine.


6. During the production of nuclear energy, various types of radioactive waste are produced. This waste is dangerous and can cause harm to people and the environment coming into contact with it.


Various Sources Of Energy

1. Nearly all the energy sources on the Earth originate from the Sun. The various sources of energy found naturally on the Earth are shown in Figure 6.13.


2. Table 6.1 explains the various sources of energy on the Earth.

Energy source

Type of energy

Energy source for daily use


* Solar energy

* Heat energy

* Solar cells convert energy into electrical energy.

* Solar panels of a solar furnace absorb solar energy as heat for heating purposes.


* Mechanical kinetic energy

* Windmills use wind power to pump water and generate electricity.


* Hydroelectric energy

* Fast flowing water can be used to generate electric energy for electrical equipment.


* Mechanical kinetic energy

* Movement of sea waves run generators and provide electricity.


* Gravitational potential energy

* Tidal barrage generates electricity.


* Heat energy inside the Earth

* Local heating.

* Steam is used to turn turbines and generate electricity.

Biomass (Plant and animal wastes)

* Biomass energy

* Food, plants, fuels for local heating.

* Operate machines and engines.


* Fossil fuels or chemical energy

* Thermal power station to generate electricity.

* Petroleum is used as the main fuel for vehicles and machines.

Radioactive substances

* Nuclear energy from fission and fusion

* Nuclear power station to produce electricity.


The Sun As The Primary Source Of Energy

1. Almost all the energy on the Earth comes originally from the Sun.


2. The Sun sends out energy as solar radiation. This solar radiation consists of light energy and heat energy.


3. Plants use solar radiation in a chemical reaction called photosynthesis to live and grow. Energy from the Sun is stored in plants as food in the form of chemical energy. This energy is then tranferred from plants to animals and humans through food chains and food webs.


4. Over millions of years, chemical and physical processes changed decayed plants and animals to fossil fuels.


5. When we burn these fossil fuels, they release heat energy. We use the heat energy to generate electricity and drive machines that are essential for our daily activities.


6. The solar radiation that heats the Earth changes the weather systems. The heated air rising above the equator causes belts of moving air around the Earth. Winds carry water vapour from oceans and bring rain. Winds can also cause sea water to move as waves.


7. Figure 6.14 below summarises how the Sun acts as the primary source of energy.


Energy Changes

1. Energy can be changed from one form into another but it cannot be created or destroyed. This is known as the law of conservation of energy.


2. When we use energy, we often convert it from one form to another.



Energy changes

Rubbing two palms together


* The palms feel hot and the sound of rubbing is heard.

* Kinetic energy → heat energy + sound energy



* The sound of clapping is heard.

* Kinetic energy → sound energy

Lighting a lamp



* The lamp lights up and becomes hot.

* Chemical energy → electrical energy → light energy + heat energy

Releasing a stretched spring


* The spring recoils.

* Potential energy → kinetic energy

Heating the joints of a copper and a zinc wire


* The galvanometer needle is deflected.

* Chemical energy → heat energy → electrical energy → kinetic energy