Energy is one of the most fundamental parts of our universe. Indeed, without energy we would not exist. If we did not eat we would not have the energy to do the things we do. Without energy in the form of electricity or gas, we cannot cook that food. The bus that takes you to school, the lights and heating in your classroom, your tv, video game etc, etc, all rely on an abundant supply of energy.

Energy is defined as "the ability to do work."

The bus is a good example of the two types of energy - Potential Energy - that is energy that is stored and - Kinetic Energy - that is energy that is moving. The fuel that powers the bus - petrol, diesel, electricity, these are all examples of potential (stored) energy. The forward momentum of the bus is kinetic (moving) energy. This is a good time to point out that:

Energy cannot be created nor can it be destroyed, it can only be changed from one form into another.

The bus changes the chemical energy (petrol) into heat and kinetic energy. How many examples of energy changes can you think of? I'll give you a few to start with:

A television set changes electrical energy into Light and Sound energy.

When switched on, a torch changes the potential battery electrical energy into light energy.

A boiling pan on a cooker is the result of electrical or gas energy being changed into heat energy.

When you use a telephone the sound of your voice is turned into electrical energy, then when it reaches the other person's phone, it is turned back into sound energy.

The Earth's atmosphere is full of energy. This energy drives the world's weather, and shapes the climates. Over the longer term, changes to this energy can bring about variations in climate. At the planetary scale, changes that are currently taking place as a result of man-made greenhouse gas emissions may be causing global warming.
All bodies emit energy in the form of electromagnetic radiation. Light is a form of electromagnetic radiation. So are infrared heat, ultraviolet radiation, radio waves and x-rays. The type of radiation emitted by a body depends upon its temperature. Hotter objects release more energetic radiation. The Sun, for example, emits visible light and ultraviolet energy. The Earth and its atmosphere, being much cooler, emit radiation in the infrared part of the spectrum. Living things, including humans, also emit radiation in the infrared part of the spectrum. This energy is known as heat energy.

The heat energy we have mentioned moves in three ways:

Conduction - This is where there is direct contact, like a saucepan placed on the oven hotplate, the heat is then directly transferred to the pan and it's contents.

Convection - This is the movement of gases or liquids from a cooler area to a warmer area. To use the saucepan example again, if you were to look at the circulation of the heated water, you would see the hotter lower layer of water rising to the colder upper layer. this is exactly what happens in the atmosphere where the warm air rises causing those thermals much loved by glider pilots. Another example is your central-heating radiator, where cold air enters the bottom and is drawn upward and heated as it passes through.

Radiation - This where the heat is transmitted by heat rays, such as the sun, or an electric fire. The central-heating radiator used in the example above also gives out radiated heat, as well as convected heat.

Different kinds of energy:

Chemical Energy

Is energy that lies in the arrangement of atoms within molecules. By rearranging the atoms, chemical reactions occur and energy may be produced or taken up. Chemical reactions usually produce heat - a burning fire is an example. Chemical energy may also be changed to electricity in a battery, and to kinetic energy in muscles.

Electrical Energy

Is energy that is given to an object by passing an electric current through it, or giving it an electrical charge. It is converted into mechanical energy in an electric motor, or heat energy in an electric fire.

Kinetic Energy

Is possessed by anything that is moving. The faster an object moves, the more kinetic energy it has. Also, the heavier an object is, the greater it's kinetic energy (but only when it is moving). Mechanical machines - cars, lathes, pile-driver or any other machines that use a motor or an engine, produce kinetic energy. This kind of energy is often called mechanical energy. Vibrating objects possess kinetic energy, and sound, which is a wave of vibrations in the air or any other substance. is a form of kinetic energy. So too is heat, because heat in an object lies in the motion of it's molecules or atoms - the hotter an object is, the faster it's molecules or atoms move. However, this form of energy is usually referred to as heat energy or thermal energy.

Nuclear Energy

Is energy produced by changing atoms within a substance. It mostly appears as heat, either under control in a nuclear reactor or in an explosion in a nuclear weapon. The Sun produces it's heat and light by nulear reactions. hence all life on Earth depends on nuclear energy, and yet, in the threat of nuclear weapons, is endangered by nuclear energy too.

Potential Energy

Is energy that an object has because of it's position. A raised hammer, a wound-up spring, a drawn archer's bow all possess potential energy. This energy is ready to be changed into other forms of energy and to do work. When the hammer falls, it will drive in a nail, the spring when released, will drive the hands of a clock and the bow will fire an arrow. As soon as any movement occurs, the potential energy decreases as it changes into energy of motion (kinetic energy). Raising the hammer, winding the spring, and drawing the bow again uses up kinetic energy and produces a gain in potential energy. In general, the higher and heavier an object is, the more potential energy it has. One of the most useful sources of potential energy is the water stored behind a dam. This water can pass through pipes and drive turbines as it falls to a lower level, changing some of the potential energy via kinetic energy into hydroelectric power.

Radiant Energy

Is energy that can cross space. It includes light, radio waves, and heat rays. Radiant heat is not the same as the kind of kinetic energy called thermal energy, but when heat rays strike an object they they cause it's molecules to move faster and it then gains thermal energy. light and heat rays are produced by making objects so hot that they glow, as in the filament of a light bulb.

Renewable Energy

Solar Power

Water Power

Hydro-electric dams are very high-tech but simple machines. A dam holds back water, creating a reservoir of potential power. On the upper side of the dam, a water gate is opened to let water surge through a tunnel leading to turbines. The power of the falling water is used to drive the turbines, which generate electricity. The electricity is carried through cables to wherever it's needed. Some hydro-electric power stations, when demand is low, use off-peak electricity to pump the water back up into the high reservoir as potential energy, to be re-used at times of peak demand.

Wind Power

The wind is used to drive giant turbines which generate electricity. The wind spins the blades just like a large toy windmilll. The blades are attached to a hub that is mounted on a drive shaft. This shaft is attached to a gear box which increases the turning speed. A high speed drive shaft from the gear box leads to the generator that makes the electricity, which is cabled to the required point. To avoid damage from extremely high winds, an in-built brake is automatically applied, stopping the rotation of the blades.