Energy

• A system is an object or a group of objects
• Energy is measured in the units of joules (J)
• The eight energy stores:

  • kinetic
  • Gravitational potential
  • Elastic potential
  • Magnetic
  • Electrostatic
  • Chemical
  • Nuclear
  • Thermal / Internal
• The kinetic energy store is the amount energy stored of a moving object
• The gravitational potential energy store is the energy stored in an object due to its height above the Earth's surface.
• The elastic potential energy store is the energy stored in an object that is stretched, squashed or compressed.
• The magnetic energy store is the energy stored when repelling poles have been pushed closer together or when attracting poles have been pulled further apart.
• The electostatic energy store is the energy stored when repelling charges have been moved closer together or when attracting charges have been pulled further apart.
• The chemical energy store is the energy stored between chemical bonds of atoms.
• The nuclear energy store is the energy stored in the nucleus of an atom.
• The thermal energy store is total kinetic and potential energy of particles in an object.
• The four energy transfers are:

  • Mechanical
  • Electrical
  • Heating
  • Radiation
• Mechanical work is a force moving an object through a distance
• Electrical work is the charges moving through a potential difference
• Heating is due to temperature difference caused electrically or by chemical reactions
• radiations is the energy transferred as a wave
• The law of conservation of energy states that energy cannot be created or destroyed, it can only be transferred from one store to another
• A closed system are sytems where neither matter nor energy can enter or leave
• Dissipated energy is energy that is not transferred to useful energy stores and is lost to the surroundings
• When a system changes, energy is transferred
• Work done is the amount of energy transferred by a force acting over a distance.
• Specific heat capacity is the amount of energy needed to raise the temperature of 1kg of a substance by 1°C
• Materials that needs to gain lots of energy in their thermal energy stores to warm up also transfer loads of energy when they cool down. They can store lots of energy.
• Power is the rate of energy transferred, or the rate of doing work
• Power is measured in watts (W). One watt = 1 joule of energy transferred per second.
• A powerful machine is one which transfers a lot of energy in a short space of time but does not necessarily mean that they can exert a strong force.
• conduction is the process where vibrating particles transfer energy to neighbouring particles
• Thermal conductivity is a measure of how quickly energy is transferred through a material through conduction. Materials with a high thermal conductivity transfer energy between their particles quickly.
• Convection is where energetic particles move away from hotter to cooler regions.
• Convection happens in gasses and liquids as they are able to move unlike solids. So, when you heat a region of a gas or liquid, the particles move faster and the space between the individual particles increase. This causes the density of the region being heated to decrease.
• As liquid and gases can flow, the warmer and less dense region will rise above denser cooler regions. If there is a constant heat source, a convection current can be created during convection
• How radiators create convection currents:

  1. Heating a room relies on creating convection currents in the air of room
  2. Energy is transferred from the radiator to nearby air particles by conduction
  3. The air by the radiator becomes warmer and less dense
  4. This warm air rises and is replaced by cooler air. The cooler air is then heated by the radiator.
  5. At the same time, the previously heated air transfers to the surroundings. It cools, becomes denser and sinks.
  6. This cycle repeats, causing a flow of air to circulate around the room, this is a convection current
• lubricants can be used to reduce friction between object's surfaces when they move
• Reducing energy transfer by heating:

  • Having thick walls that are made from a material with low thermal conductivity. The thicker the walls and the lower the thermal conductivity, the slower the rate of energy transfer will be.
  • use thermal insulation
• Loft insulation

  • Reduces convection currents in loft
• Double glazed windows

  • Have an air gap between two sheets of glass to prevent energy transfer by conduction through windows
• Draught excludes around doors and windows

  • Reduce energy transfers by convection
• Cavity walls

  • Made up of inner and an outer wall with an air gap in middle
  • The air gap reduces the amount of energy transferred by conduction through the walls
• Cavity wall insulation

  • The cavity wall air gap is filled with foam
  • Can also reduce energy transfer by convection through the wall cavity
• A useful device is only useful because it can transfer energy from one store to another. The less energy that is wasted in this energy store, the more efficient the device is. The efficiency of energy transfer can be improved by insulating objects, lubricating them, or making them more streamlined