Energy can change from one form to another, and frequently does.

Chemical energy in food turns into kinetic energy for movement;

Electrical energy in a circuit turns into heat energy in a resistor;

Kinetic energy in your muscles turns into sound energy from you voice.

Elastic potential energy in a taught rubber band turns into kinetic energy when it sails through the air.

For example, when you switch on a light, you are not loosing energy from a battery (chemical), you are just converting it to light energy!

With all devices that aim to use energy for a reason, some of the energy put in to run it comes out as a non useful form of energy.

The more energy that comes out as useful, the more efficient the object is.

a light bulb wants to create light energy, but it creates heat at the same time.

Conduction is when energy is passed from one particle to another via contact. For example heat is passed from your skin to a window when they touch.

Convection is when particles with energy rise, the space they leave is filled by other particles. If the source of energy continues these new particles will also gain energy, they will then rise and the process will be repeated.

Radiation is when heat is transferred as infra red waves. These waves can travel through space and be conducted or reflected.

Convection is helpful as it distributes heat energy. This is useful in many situations, for example, a radiator in one place will be able to heat a whole room, as hot air will rise away from it creating a current of cool air to be heated.

If something with heat energy is surrounded by an insulator, it wont lose heat by conduction.

in buildings where insulating materials are put in walls and on floors to stop heat being lost from inside.

This is the same in humans where we wear clothes to stop heat being lost from conduction.

Air is a poor conductor, so materials with many air gaps in are also poor conductors; air trapped between double glazing prevents heat loss through windows.

At the top of the swing, it will have its highest gravitational potential energy (as its further from the earth); but it will have its lowest kinetic energy (it slows to a stop at the top point).

At the bottom of the swing, it will have its lowest gravitational energy (as it is closer to the earth); but it will have its highest kinetic energy (it goes very quickly past the bottom point).

Between the points work (force x distance) is constantly being done: the pendulum is moving through space.

Remembering that work done is equal to energy transferred, we can see that as work is done that moves the pendulum upwards, kinetic energy is transferred in to gravitational potential energy. When work is done to bring the pendulum downwards, energy is transferred from GPE to KE.

The pendulum demonstrates that energy is conserved, as then energy is constantly changing between different forms. The only reason that energy is lost from the pendulum, and it slows down, is that some energy is transferred into heat or sound.