Energy

• Energy

  Never created or destroyed, only transferred between different forms and objects
• Forms of energy

  • Thermal or internal energy
  • Kinetic energy
  • Gravitational potential energy
  • Elastic potential energy
  • Chemical energy
  • Magnetic energy
  • Electrostatic energy
  • Nuclear energy
• Energy transfer

  1. Mechanical

  2. Electrical

  3. Heating

  4. Radiation (light or sound waves)
• Open system

  Can exchange energy with the outside world
• Closed system

  Separate from the outside world, neither matter nor energy can enter or leave
• Work done

  Energy transferred
• Types of work done

  • Mechanical
  • Electrical
• Kinetic energy

  The energy that an object possesses due to its motion
• Kinetic energy

  • Depends on an object's speed
  • Depends on an object's mass
• Faster an object is moving

  More kinetic energy it will have
• More mass an object has

  More kinetic energy it will have
• Gravity

  A force of attraction between two objects, with the size of the force depending on the mass of the objects and the distance between them
• For small objects like apples or buildings, the gravitational force of attraction is tiny as they have relatively low masses
• For very large objects that are far away like Jupiter, the gravitational force is also tiny due to the large distance
• For very large objects that are close by like the Earth or Moon, gravity is felt more strongly and has a big influence on nearby objects
• Gravitational field

  The field of influence around an object
• Gravitational field strength

  The strength of the gravitational field, denoted by the letter g
• The gravitational field strength on Earth is around 9.8 Newtons per kilogram
• The gravitational field strength on the Moon is 1.6 Newtons per kilogram
• Weight

  The force of attraction experienced by an object in a gravitational field
• Calculating weight

  Mass x Gravitational field strength
• Gravitational potential energy

  The energy an object has due to its position in a gravitational field
• Calculating gravitational potential energy

  Mass x Gravitational field strength x Height
• Conservation of energy principle

  Energy can be transferred, usefully stored or dissipated, but can never be created or destroyed
• Energy can only move between different objects and different forms
• Open system

  • Energy and matter can freely move between the system and the environment
• Closed system

  • Energy and matter can't enter or escape the system
• The overall energy of a closed system doesn't ever change
• Reducing unwanted energy transfers

  1. Using thermal insulation

  2. Using lubrication
• Reducing heat loss in a house

  1. Make the house sealed closed to prevent air passing out (reduce heat loss by convection)

  2. Reduce heat loss by conduction through walls and windows (use materials with low thermal conductivity, cavity walls with insulating foam)

  3. Reduce heat loss through windows (use double glazing)
• Conduction

  Heat is lost directly through a solid like a wall or a window
• Convection

  Heat is transferred through liquids and gases
• Friction

  The resistance that an object encounters when moving over a solid or through a fluid
• Friction reduces the efficiency of energy transfer

  Can cause objects to heat up
• Reducing friction

  1. Adding oil (a lubricant)

  2. Making cars and planes streamlined (reduces air resistance)
• Power

  The rate at which energy is transferred
• Power

  The rate at which work is done
• Calculating power (energy transfer)

  Power = Energy transferred / Time taken
• Calculating power (work done)

  Power = Work done / Time taken
• Work done is a special measure of the energy transferred when a force is used to move an object by a certain distance