Energy, work and power

• Name 8 energy stores

  kinetic, thermal, chemical, gravitational potential, elastic potential, electrostatic, magnetic, nuclear energy
• Name 4 energy transfers

  mechanically

  electrically

  by heating

  by radiation
• what is the principle of conservation of energy?

  energy cannot be created or destroyed but can be transferred from one store to another
• Some energy is always wasted when it is transferred from one store to another.

  Equation: total energy in = useful energy out + wasted energy
• What is a system?

  A system is an object or group of objects within which energy is transferred
• What is an open system?

  A system where energy can be transferred between the system and the surroundings
• What is a closed system?

  A system where there is no energy transferred between the system and the surroundings. Energy will only change inside
• What is thermal conductivity?

  the rate at which energy is transferred through a material
• what happens to the temperature of an object when work is done against friction?

  the mechanical energy turns into thermal energy (heat).

  the temperature of an object increases
• what are the energy transfers when an object is projected upwards?

  kinetic energy to gravitational potential energy upwards

  then gravitational potential energy to kinetic energy on the way down
• what are the energy transfers and stores when a moving object hits an obstacle?

  kinetic energy is transferred to thermal energy due to friction. Then possibly elastic potential energy
• what are the energy transfers and stores when an object is accelerated by a constant force?

  kinetic energy store and possibly thermal
• what are the energy transfers and stores of a vehicle slowing down?

  kinetic energy to thermal energy of the brakes
• what are the energy transfers and stores of an electric kettle boiling water?

  electrical energy to thermal energy
• what is wasted energy?

  energy that can be lost when being transferred, for example, energy can be wasted as heat or sound
• What is the definition of a Joule?

  1J = 1 Nm
• What is Hooke's law?

  The extension of an elastic object, such as a spring, is directionally proportional to the force applied provided that the limit of proportionality is not exceeded.

  The equation: force = spring constant x extension
• what is power?

  the rate at which energy is transferred or the rate at which work is done.

  Power = work done/time
• the total amount of energy is systems remains constant though the way the energy is stored in the system can change so energy can be transferred
• the energy transferred in a system are not useful as energy could be wasted
• Unwanted energy transfers can be reduced in a number of ways for example through lubrication and the use of thermal insulation
• Describe ways to increase the efficiency of an intended energy transfer

  reduce friction by using lubrication, thermal insulation , use more efficient devices, streamline moving objects, use electrical components efficiently and recover waste energy
• Describe the main energy resources available for use on Earth

  fossil fuels

  nuclear fuel

  biofuel

  wind

  hydroelectricity

  the tides

  the sun
• What is the definition of renewable energy sources?

  Energy resources that are naturally replenished in a short time
• What is the definition of non-renewable energy sources?

  energy resources that will run out because they take millions of years to form