energy ⚡️

• types of energy store:

  1. thermal
  2. kinetic
  3. gravitational potential
  4. elastic potential
  5. chemical
  6. magnetic
  7. electrostatic
  8. nuclear
• when a system changes, energy is transferred
• energy can be transferred:

  • into the system
  • away from the system
  • between different objects in the system
  • between energy stores
• closed system: a system where neither matter nor energy can enter or leave
• the net change in a closed system is always 0
• energy can be transferred:

  • mechanically (a force doing work)
  • electrically (work done by moving charges)
  • by heating
  • by radiation
• work done: another way of saying energy transferred
• work can be done:

  • when current flows
  • by a force moving an object
• anything that is moving has energy in its kinetic energy store
• energy is transferred into the kinetic energy store when the object speeds up
• energy is transferred away from the kinetic energy store when the object slows down
• the amount of energy in the kinetic energy store depends on the object’s mass and speed
• the greater the object’s mass, the more energy in its kinetic energy store
• lifting an object in a gravitational field requires work to be done
• when you lift an object in a gravitational field, energy is transferred to the gravitational potential energy store of that object
• the amount of energy in the gravitational potential energy store depends on the object’s mass, height and the strength of the gravitational field
• if an object falls, energy from its gravitational potential energy store is transferred to its kinetic energy store
• if a falling object experiences no air resistance, the energy lost from the gravitational potential energy store will be equal to the energy gained in the kinetic energy store
• stretching or squashing an object can transfer energy to its elastic potential energy store
• specific heat capacity: how much energy is needed to heat 1kg of something up by 1 degrees celsius
• the specific heat capacity of water is 4200 J/kg
• energy cannot be created or destroyed, only transferred
• when energy is transferred between stores, not all of it is transferred usefully and some is always dissipated
• dissipated energy can be called wasted energy because it is being stored in a way that is not useful
• power: the rate of doing work
• power is measured in watts
• 1 watt = 1 joule of energy transferred per second
• conduction: the process where vibrating particles transfer energy to neighbouring particles
• solids transfer energy via conduction
• liquids and gases commonly transfer energy via convection
• conduction:

  1. energy transferred to an object by heating is transferred to the thermal store of the object
  2. the energy is shared across the kinetic energy stores of the particles in the object
  3. the particles in the part of the object being heated vibrate more and collide with each other
  4. these collisions cause energy to be transferred between particles’ kinetic energy stores
  5. the process continues throughout the object until the energy is transferred to the other side of it
  6. the energy is transferred to the thermal energy store of the surroundings or anyone who’s touching the object
• thermal conductivity: a measure of how quickly energy is transferred through a material via conduction
• convection: where energetic particles move away from hotter to cooler regions
• convection does not happen in solids
• convection:

  1. energy is transferred by heating to the thermal store of the liquid or gas
  2. this energy is shared across the kinetic energy stores of the gas or liquid’s particles
  3. the particles are able to move so they move faster and the space between particles increases
  4. the density of the region begins to decrease
  5. liquids and gases can flow so the warmer and less dense region will rise above denser cooler regions
  6. if there is a constant heat source a convection current might be created
• convection currents:

  1. energy is transferred from the heat source to nearby particles via conduction
  2. the liquid or gas near the heat source becomes warmer and less dense because the particles are moving quicker
  3. the warm liquid or gas rises and is replaced by cooler liquid or gas
  4. the cooler liquid or gas is then heated by the heat source
  5. the cycle repeats