P1

• a system is an object or group of objects
• a closed system is one where no energy can escape to or enter surroundings; total energy in a closed system never changes
• kinetic - energy an object had bc. it’s moving
• gravitational potential - energy an object has bc. of its height above ground
• elastic potential - energy an elastic object has when stretched or compressed
• thermal - aka internal; energy an object has bc. of its temperature (total kinetic and potential energy)
• chemical - energy that can be transferred by chemical reactions involving foods, fuels and batteries
• nuclear - energy stored in nucleus of atom
• magnetic - energy a magnetic object has when it’s near a magnet or magnetic field
• electrostatic - energy a charged object has when near another charged object
• Energy transfers:

  • heating - from one object to another with a lower temperature
• Energy transfers:waves - e.g. light and sound waves transfer energy by radiation
• Energy transfers: electricity - when an electric current flows it can transfer energy
• Energy transfers: mechanical work - energy transferred when a force moves or changes shape of object
• when rubber band is stretched, energy from chemical store is mechanically transferred to band’s elastic store
• electric current in a kettle transfers energy to heating element’s thermal energy store; energy is then transferred from heating element’s thermal store to water’s thermal store
• • energy cannot be created or destroyed, only transferred
  • dissipated energy is often described as wasted
  • energy is never entirely usefully transferred
  • all energy ends up eventually in thermal store of surroundings
• in machines, work done against friction usually causes wasted energy bc. energy is transferred to thermal store of machine and surroundings
• Lubrication is a way of reducing friction
• Streamlining is a way of reducing air resistance or drag in water
• Thermal insulation is a way of reducing energy wasted due to heat dissipating to surroundings
• Efficiency is a measure of how much energy is transferred usefully
• Power is how much work is done or energy transferred per second; work done = energy transferred; unit of power is Watt
• • gravitational potential energy = GPE / Ep

  change in GPE = mass (kg) x gravitational field strength (N/kg) x height (m)
• • kinetic energy = KE / Ek

  change in KE = 1/2 x mass (kg) x velocity² (m/s)
• • power (W) = energy transferred (J) ÷ time taken (s)

  or power (W) = work done (J) ÷ time (s)
• • elastic potential energy = EPE / Ee

  change in EPE = 1/2 x spring constant (N/m) x extension² (m)
• efficiency (%) = useful output energy (J) ÷ total input energy (J)