Conservation and Dissipation of Energy

• A system is an object or group of objects.
• There are changes in the way energy is stored when a system changes.
• An object projected upwards by a slingshot:

  • elastic potential energy
  • gravitational potential energy and kinetic energy
• A moving object hit by an obstacle:

  • kinetic energy
  • thermal energy and sound waves
• An object accelerated by a constant force:

  • increase in kinetic energy
• A vehicle slowing down:

  • decrease in kinetic energy
• Bringing water to a boil in an electric kettle:

  • current in heating element
  • transfers energy to thermal store of the water and kettle
• Energy can be transferred usefully, stored or dissipated. It cannot be created or destroyed.
• When there are energy transfers in a closed system, there is no net change to the total energy.
• In all system changes, energy is dissipated so it is stored in less useful ways.
• To reduce unwanted energy transfers, you could use lubrication to reduce friction between moving parts, tighten loose parts to reduce vibrations and reduce noise by streamlining the shape of an object.
• Kinetic energy stores describe the energy that an object has because it is moving.
• Elastic potential energy stores describe the energy that is stored in a springy object and when you squash or stretch it.
• Limit of proportionality is the limit that the elastic object no longer returns back to its original shape.
• Gravitational potential energy stores describe the energy that is stored in an object because of its position about the ground. Objects with mass have weight due to gravitational field strength.
• Thermal energy stores describe the energy a substance has because of its temperature.
• The specific heat capacity of a substance is the amount of energy required to raise the temperature of 1kg of a substance by 1°C.
• Power is the rate at which energy is transferred or the rate at which work is done.
• An energy transfer of 1 joule per second is equal to a power of 1 watt.