Transferring Energy

Energy can be transferred from one place to another or converted between different forms, but it can never be created or destroyed; this is the law of conservation of energy.
Examples of energy transfer include a bulb transforming electrical energy into light and thermal energy, and a person eating food, which is then converted into kinetic energy when they move.
Energy can be transferred usefully, stored or dissipated (spread out and lost to the surrounding environment). A car engine, for example, turns fuel into kinetic energy to move the car, but also produces waste heat and sound.
Mechanical energy transfer often involves forces. When a force moves an object, work is done on the object and energy is transferred.
The work done on an object can be calculated using the formula: Work done (Joules) = Force (Newtons) x Distance moved (metres). In this formula, a Joule (J) is the unit of energy or work done, a Newton (N) is the force necessary to accelerate 1 kg of mass at 1 m/s², and distance is measured in metres.
Gravitational potential energy is energy an object possesses due to its position in a gravitational field. The higher an object is lifted, the greater its gravitational potential energy.
Kinetic energy is the energy possessed by an object due to its motion. The amount of kinetic energy an object has can be calculated using the formula: Kinetic energy (Joules) = 0.5 x Mass (kilogrammes) x Speed² (metres per second)².
Electrical energy is transferred when charges move in a wire. The unit of electrical energy is the joule, which is the energy transferred by a one joule of work. However, kilowatt-hour (kWh) is often used in practise, as it is a larger and more practical unit.
Chemical energy is stored in the bonds of chemical substances. It can be released in chemical reactions, often in the form of heat; this is used in cooking, for example.
The efficiency of an energy transfer can be calculated using the formula: Efficiency = Useful energy output / Total energy input, which is then often multiplied by 100 to give a percentage. Energy efficiency measures how much of the total energy is actually converted into the desired form of energy.