P1

• Energy store


  A 'type' of energy that is stored in a specific way in an object
• Energy cannot be created or destroyed but it can be transferred, dissipated or stored in different ways
• Energy stores


  • Magnetic
  • Thermal
  • Chemical
  • Kinetic
  • Electrostatic
  • Elastic potential
  • Gravitational potential
  • Nuclear
• System

  An object or objects that can store energy in them
• Closed system

  An isolated system in which no energy transfers take place out of or into the energy stores in the system
• Energy transfer


  1. Mechanically (when a force moves through a distance)

  2. Electrically (when a charge moves due to a potential difference)

  3. By heating (because of a temperature difference)

  4. By radiation (e.g. Light, microwaves, sound)
• Energy flow diagram


  • Example of a gas cooker
• The law of conservation of energy states that energy cannot magically disappear or be destroyed
• Energy is always conserved (maintained) at a constant overall amount
• In a closed system with no air resistance or friction

  All the gravitational potential energy would transfer to the kinetic energy store as the pendulum swings downwards, and all the kinetic energy would transfer to the gravitational potential energy store as the pendulum swings upwards

  
• In an open system

  The pendulum would lose its original swinging height and eventually come to a complete stop due to energy being transferred to the surroundings from friction and air resistance
• Bungee jump


  1. Gravitational potential energy transferred to kinetic energy

  2. Kinetic energy transferred to elastic potential energy in the rope

  3. Elastic potential energy transferred back to kinetic energy and then to gravitational potential energy
• In the bungee jump example, 900J was transferred to elastic potential energy and 100J was transferred to the surroundings
• The total energy before the jump (1000J) equals the total energy after the jump (900J + 100J)
• This example obeys the principle of the conservation of energy
• Energy transfers in a bungee jump

  1. Gravitational potential energy transferred to elastic potential energy in the rope

  2. Elastic potential energy transferred back to kinetic energy as the jumper springs back upwards

  3. Kinetic energy transferred back to gravitational potential energy
• The conservation of energy explains the transfers of energy in a bungee jump
• Using numbers can help to explain the law of conservation of energy
• Energy transfers in a bungee jump example

  1. Before: Jumper has 1000 J of gravitational potential energy

  2. After: 900 J transferred to elastic potential energy, 100 J transferred to the surroundings
• The example obeys the principle of conservation of energy - energy has not been created or destroyed
• The law of conservation of energy applies to all systems, whether closed or open
• Energy cannot be created or destroyed
• Conservation of energy applies to all energy transfers
• Energy can be transferred between energy stores within a closed system, with the total energy remaining the same before and after the transfer
• System


  A defined physical or conceptual entity
• Closed system


  A system that does not exchange energy or matter with its surroundings
• Law of conservation of energy


  Energy cannot be created or destroyed, it can only be transferred or transformed
• Standard units


  Units used in the scientific community across the world, seen as a universal language despite scientists speaking and writing in different languages
• Standard units are important as it allows for the study and direct comparison of numerical data from investigations
• Each measurement in physics has a standard unit
• There are other units that are sometimes used, but if you see different units in the exam you will need to convert them into the standard units
• Worked example using the Ep = m g h equation


  1. Mass = 0.5 kg

  2. Gravitational field strength on Earth = 9.8 N/kg

  3. Height = 6 m

  4. Ep = m g h

  5. Ep = 0.5 x 9.8 x 6

  6. Ep = 29.4 J

  
• Gravitational potential energy store


  • Increases when an object moves up and decreases when it moves down
  • Increases when an object is lifted up because work is done on it to overcome the gravitational force

  
• The gravitational field strength at the surface of the Moon is less than on the Earth
• Change in the gravitational potential energy store of an object


  Ep = m g h

  
• Kinetic energy


  The energy stored in an object because it is moving
• Kinetic energy store


  Depends on the speed of the object and the amount of matter contained in the object (its mass)
• The faster an object moves, the more kinetic energy it has
• The more mass an object has, the more kinetic energy it will have
• Kinetic energy equation


  Ek = 0.5 m v^2