Energy

• Energy cannot be created or destroyed, only transferred.
• moving objects = kinetic store

  warm objects = thermal store

  chemical (food, muscles, fuels, e.c.t) = chemical store

  objects at a height = gravitational potential store

  stretched objects = elastic potential store

  magnets attracting/repelling = magnetic store
• mechanical - when a force is applied to move an object through a distance
• electrical - when charge flows through a circuit
• heating - when energy is transferred between hotter and colder areas
• radiation - when energy is transferred as a wave, e.g. light/sound
• Energy is measured in joules.
• internal energy - the total amount of kinetic energy and potential energy of all the particles
• When a substance melts or evapourates, energy is used to break intermolecular bonds. The stronger the bonds are, the more energy needed to break them. This causes higher melting and boiling points.
• temperature - measure of how hot something is
• thermal energy - type of energy store, is always transferred from hotter to colder areas/objects
• conductors - materials that allow charge/heat to pass through them easily
• insulators - materials that do not allow charge/heat to pass through them easily
• There are four energy transfers/pathways : mechanical, electrical, by heating/contact, radiation
• dissipation - the wasted energy (usually thermal) transfer of energy (usually to the surroundings)
• The amount of electrical energy depends on:

  • the power of the appliance
  • the time for which the appliance is working
• cost of electricity = power x time x cost per kwh

  (kw) (hr) (p)
• efficiency - the ratio of useful energy transfer to wasted energy (dissipation)
• efficiency = useful energy transferred/total energy supplied

  (no units) (joules - J) (joules - J)