We use energy to do work. When we play for a long time we feel tired, and our ability to work is reduced. Energy is the capacity or ability to do work. Whether we do physical work, mental work or mechanical work, energy is always used.
We have learnt that every change involves energy. Energy is all around us. Our energy comes from the food we eat. Food, therefore, must have energy. Energy is not mater. No on has ever seen or tasted or smelled energy. But this does not mean that energy does not exist.
All the electric appliances work only when an electric current is passed through them. Electricity can heat things, produce light and sound; it can make things move. Thus electricity can perform various kinds of work and has different forms of energy.
The wind has energy. This energy is used to propel sailing boats and to turn the blades of windmills. Running water has energy. It is capable of moving rocks and pebbles along a river-bed. Motor cars get energy from petrol.
Thus it follows that energy appears in different forms. Anything that can cause change has energy.
Relationship between Work and Energy:
A body possessing energy is capable of doing work. Also, the work done on a body gets stored in the form of its energy and this energy in the body can be used to do some work.
Forms of Energy:
- Mechanical energy
- Chemical energy
- Heat energy
- Light energy
- Sound energy
- Electrical energy
- Magnetic energy
- Atomic energy
- Solar energy
- Muscular energy
1. Mechanical energy:
Mechanical energy is the energy stored in a body. It is of two kinds:
1. Potential energy, 2. Kinetic energy
- Potential energy: is the energy stored in a body when it is at rest. It is because of its position or condition. The energy possessed by a raised body is potential energy due to its position relative to ground. A stretched rubber band has potential energy because of its condition.
- Kinetic energy: is the energy stored in a body while it is in motion.
All moving objects have kinetic energy. A moving bullet has kinetic energy. Wind, storm and running water possess kinetic energy.
For example an arrow on a stretched bow has potential energy because it is at rest. It has kinetic energy when it is in motion after its release. Similarly, a small stone on stretched catapult has potential energy.
Springs store potential energy because of their condition when they are stretched, compressed, or twisted. When they return to their original condition, this stored energy is released. Potential energy cannot do work until it has been transformed into kinetic energy.
2. Chemical Energy:
When a matchstick is rubbed against a matchbox it burns giving heat and light. The chemical reaction starts when the matchstick is rubbed. When the chemical substances are used up, the chemical reaction stops. The energy within the head is due to its chemical composition. The energy stored in the molecules of the chemicals called chemical energy. Wood, coal, petrol, kerosene and diesel oil all contain chemical energy. This energy is converted into heat energy when the fuel burns.
3. Heat Energy:
Heat is a form of energy possessed by a substance because of the motion of its molecules. When we heat water in a beaker covered with a lid the water molecules from the bottom move up. Thus, water molecules gain kinetic energy. When we continue to heat, water boils and the lid moves up and down. It happens due to heat energy of the steam. Heat energy of steam has tremendous capacity to do work. James Watt used this idea to invent the steam engine.
4. Light Energy:
Light is a form of energy. It can cause changes and make things move. When light falls on a photographic film, it cause chemical reactions. Due to this change, an image of the objects recorded permanently. Plants also use sun’s light energy to make food.
5. Sound Energy:
Sound is another form of energy as it can make things move.
- When we talk, our sound produces vibratory motion. Touch the front part of your throat when you talk. You will feel vibrations. Vibrations are back-and-forth motions of the vibrating body.
- Hold your hand in front of the speaker of a radio while it is turned on. You will feel the vibrations of the speaker and the air in front of it.
- When an aeroplane passes over your house, you feel vibrations of the windows of your house. Similar vibrations are feeling when a railway train passes near the house.
Vibrating objects produce sound. When you pluck the string of a sitar you continue to hear sound as long as the string vibrates. Similarly, when we hit the skin of a drum, the skin starts vibrating very rapidly and we are, thus, able to hear sound. Vibrations in the air reach our ears and we hear sound. Sound is possible only in material media-solid, liquid, or gas. Sound cannot be produced or heard in vacuum.
6. Electrical Energy:
Electricity is a form of energy. It can produce motion. It can cause changes. It can heat or cool our homes, cook our food, operate electrical gadgets and move our vehicles.
A battery in an automobile supplies electric current to start the motor. Dry cells are used in torches, radios, quartz watches and clocks. They give electric energy.
7. Magnetic Energy:
Magnetic energy is another form of energy. It can cause motion. A magnet pulls iron pieces. A crane which uses a strong magnet can load and unload heavy iron from a ship. This is an example of magnetic energy. Telephones, headphones, electric fans, electric bells, etc., are electric machines which use magnets producing magnetic energy. Magnetic energy is always associated with electrical energy. Electrical energy is transformed into magnetic energy and vice versa.
8. Atomic Energy:
Chemical energy is the energy hidden in the molecules of the substances. Atomic energy is the energy bidden in the atoms of the substances. Atoms have a large amount of energy. A few atom bombs can destroy the whole world. Atomic energy can be converted into electrical and other forms of energy.
9. Solar Energy:
The sun gives you heat and light. Plants use the light energy of the sun to make food. Plants are the source of food for animals. Since plants get their energy from the sun, the sun is a source of energy for animals. In fact, the sun is the ultimate source of energy. The energy we get from the sun is called solar energy.
Nowadays, solar energy is being utilized in different forms. Solar cookers and solar heaters are being used to cook food and supply hot water. Solar cells convert sunlight into electricity. They are used in satellites to provide energy.
10. Muscular Energy:
Muscular energy is another from of energy. Food that we eat has chemical energy stored in it. This is converted in our system info muscular energy. Due to this energy, we feel more energetic and are able to do a lot more work. Animals, such as horses, camels and bullocks use their muscular energy to do useful work for us.