Energy And Sources Of Energy | Grade 7 Science Lesson
Energy
When we do some work, we are using energy. Without energy, we cannot do any kind of work. So, energy is the capacity to do work. Joule is the S I unit of energy (J). Energy is needed to perform activities.
Sources of energy
The Sun
The principal provider of energy for the earth is the Sun. Sun is directly or indirectly the source of most of the energy that living beings use.
Light energy from the Sun
Plants are direct utilizers of light energy from the sun to make food. Most animals consume plants to obtain energy for their daily activities.
Wood from plants can be burnt to provide energy.
Heat energy from the Sun
Heat energy from the Sun is used to provide warmth for living organisms. It is also used to dry your clothes.
Fossil fuels
Do living things turn into something else when they die? Do they generate other living beings? No. But they are still useful even though dead. Subject to heat and pressure, the remains of dead animals and plants transform into fossil fuels over millions of years. Can we use these fossil fuels in their original form? No. We create usable sources of energy out of fossil fuels.
The diagrams below illustrate the formation of fossil fuels.
300 million years ago, the earth was populated with animals.
Plants and animals that died were buried on the ocean floor.
Over millions of years, the remains of plants and animals may turn into crude oil and gas due to high pressure and heat.
Million of years later, the crude oil and gas are extracted to be used as energy sources.
Crude oil is obtained from the deep underground. It is then separated in an oil refinery into many types of fuel. Crude oil can be used for cooking (as gas), diesel fuel for vehicles, bitumen, kerosene, petrol, heavy oil fuel and lubricating oil.
Natural gas
Natural gas is also found under the sea. It is used in homes and factories to fuel heating. Natural gas is also used a fuel in power stations to generate electricity.
Coal
Coal is procured from mining deep underground. It is used in power stations to produce electricity.
Forms of energy
The chart below summarizes different forms of energy in a succinct way.
Potential energy
When something has potential energy, it means that it has the potential to release energy. There are three main kinds of potential energy. Let us see what they are.
1. Chemical potential energy
The energy stored in substances that can be released through chemical reactions is called chemical potential energy. Have you used a torch light with batteries? Those batteries have chemical potential energy. Even our bodies contain chemical potential energy.
2. Gravitational potential energy
The energy an object has because of its position or location is called gravitational potential energy. This is why when something that falls from a high position can damage whatever it hits.
3. Elastic potential energy
The energy an object has when it is stretched or compressed is called elastic potential energy. Have you been hit by a friend with a stretched rubber band? Well, you know now why it hurt so much!
Kinetic energy
The energy that an object has due to its movement is called kinetic energy. Have you been incapacitated by being hit by a moving object? Well, you know!
Electrical energy
Have you watched lightning during thunderstorms? It is a form of electrical energy. Many modern appliances run on electrical energy. And it is absolutely essential for modern life in many ways.
Heat energy
Melting metals, creating steam to turn turbines and making chemicals react are a few of the industrial uses of heat energy. Of course, in homes heat energy is used in cooking, ironing clothes etc.
Light energy
The Sun provides light for the earth. You might ask “how about fireflies?” True enough, living organisms such as the firefly give out light energy on their own.
Sound energy
Sound energy is the energy that can be heard. It is caused by vibrations of matter such as the vibrations of guitar strings, piano strings and car engines. Sound travels from one place to another because air particles also vibrate. Therefore, sound cannot travel through a vacuum.