P.1 - Conservation and Dissipation of Energy

Changes in Energy Stores

  • A system is an object or a group of objects

  • Kinetic energy store - e.g. someone running - more energy when an object moves faster

  • Thermal energy store - e.g. oven - more energy when object gets hotter

  • Chemical energy store - e.g. food / battery - more energy when transfers more energy when reacting

  • Gravitational Potential energy store - e.g. pen being held aloft - more energy when greater mass, higher up

  • Elastic Potential energy store - e.g. stretched elastic band - more energy when object is held taught

  • Electrostatic energy store - e.g. electrons and protons repelling - more energy when larger charge

  • Magnetic energy store - e.g. magnets repelling - more energy when magnets are stronger

  • Nuclear energy store - e.g. bombs - more energy when transferring more energy when reacting

  • When EVENT, energy is transferred from the INITIAL ENERGY STORE of OBJECT to the FINAL ENERGY STORE of OBJECT

  • Mechanical, electrical, radiation and heat are all energy transfer pathways

Equations

  • Work done = Force x Distance / W = FS

  • Weight = mass x gravitational field strength (g.f.s) / W = mg (g.f.s = N/Kg)

  • Gravitational potential energy = mass x g.f.s x height / Ep = mgh

  • Kinetic energy = ½ x mass x mass x speed2 / Ek = ½ mv2

  • Elastic potential energy = ½ x spring constant x (extension)2 / Ee = ½ ke2 (extension = m) (spring constant = N/m)

  • Efficiency = useful output transfer / total input energy transfer (efficiency = no unit)

  • Efficiency = useful power output / total power input

  • Useful energy out = total energy in - ‘wasted energy’

  • Power = energy transferred / time / P = E/t

  • Power = work done / time / P = W/t

Other

  • Useful energy is energy transferred to where it is wanted in the way it is wanted

  • Wasted energy is energy that is not usefully transferred

  • In numerous cases, friction is the cause of energy being wasted

  • Mass is the amount of matter in an object

  • Wight is the force acting on an object due to gravity

  • Kinetic energy is a store of energy du to the movement of an object

  • Efficiency is the proportion of input transfer which is usefully transferred

  • It is not possible to have an efficiency greater than 1

  • Power is the rate at which energy is transferred or the rate at which work is done

  • Energy transfer of 1 Joule per second is equal to a power of 1 Watt

  • 3 main ways appliance work:

    o Motors

    o Heating elements

    o Speakers (electromagnet)