Energy

• Energy

  A physical quantity that can be measured, the joule is a commonly used unit
• Different stores of energy


  • Kinetic
  • Gravitational potential
  • Chemical
  • Elastic (strain)
  • Nuclear
  • Electrostatic
  • Internal (thermal)
• Energy transfers


  1. By heating

  2. By forces or mechanical work done (i.e. mechanically)

  3. By electric currents or electrical work done (i.e. electrically)

  4. By electromagnetic waves

  5. By sound waves
• Kinetic energy


  Energy of a moving object, calculated using the formula 1/2mv^2
• Gravitational potential energy


  Energy of an object at a height above the ground, calculated using the formula mgh
• Principle of conservation of energy


  Energy cannot be created or destroyed, it can only be transferred from one store to another
• Energy transfers in an ideal pendulum

  1. Gravitational potential store at A transferred mechanically to kinetic store at B

  2. Kinetic store at B transferred mechanically to gravitational potential store at C
• Maximum speed of an ideal pendulum


  Depends on the height, not the mass
• In the real world, a swinging pendulum will eventually come to a stop
• Not all energy input can be fully transferred into useful energy, some is dissipated as wasted energy
• Energy is the ability to do work
• The energy transfer diagram shows how much energy has been transferred from one store to another.
• A closed system is when there are no exchanges with its surroundings, while an open system allows exchanges between itself and its surroundings.
• Work done by a force = force x distance moved (J)
• Power = work done/time taken
• An open system is when matter or energy can enter or leave the system
• An isolated system does not allow any exchange of matter or energy with its surroundings.
• Kinetic energy (KE) is the energy that an object possesses due to its motion.
• Potential energy (PE) is the stored energy that an object possesses due to its position or configuration.
• Power (W) = electrical energy (J)/time taken (s)
• 1 Joule = 1 Newton metre (Nm) or 0.239 calories (cal)
• 1 Watt = 1 Joule per second (J/s)
• Kinetic energy = ½ mass x velocity²
• Energy cannot be created or destroyed but it can change form.