3.3 Work, Energy and Power

Work done

the amount of energy transferred from one form to another when a force moves an object through a distance or when a charged particles moves through a potential difference

Joule

one joule is the work done when a force of 1 newton moves an object through a distance of 1 metre

Principle of conservation of energy

energy cannot be created or destroyed. Energy can be transferred from one form to another but the total amount of energy in a closed system will not change.

Closed system

can't lose energy to surroundings

Kinetic energy

energy due to motion of an object with mass e.g. moving car

Electromagnetic energy

energy associated with all EM waves, stored within the oscillating electric and magnetic fields e.g. energy from Sun/LED

Sound energy

energy of mechanical waves due to the movement of atoms e.g. energy emitted when you clap, output energy from headphones

Thermal energy

the sum of the random potential and kinetic energies of atoms in a system e.g. a hot cup of tea has more thermal energy than a cold one (both kinetic and potential)

Gravitational potential energy

energy of an object due to its position in a gravitational field e.g. child at top of slide, water held in clouds

Chemical energy

energy contained within the chemical bonds between atoms - it can be released when the atoms are rearranged e.g. energy stored within a chemical cell, energy stored in petrol and released when it's burnt

Elastic potential energy

energy stored in an object as a result of reversible change in its shape e.g. stretched guitar string, squashed spring

Electrical potential energy

energy of electrical charges due to their position in an electric field e.g. electrical charges on a thundercloud, static charge on a charged balloon

Nuclear energy

energy within the nuclei of atoms - it can be released when the particles within the nucleus are rearranged e.g. energy from fusion processes in the Sun, energy from nuclear fission reactors

Power

rate of doing work, amount of energy transferred from one form to another per second

Watt (W)

rate of energy transfer equal to 1 joule per second (Js-1)

Efficiency

ratio of useful energy given out by a mechanical system to the amount of energy put into the system