Chp 9: Energy & Work done

• Energy


  The ability to do work
• SI unit for energy

  Joule (J)
• Forms of energy


  • Kinetic energy
  • Gravitational potential energy
  • Elastic potential energy
  • Chemical potential energy
  • Electrical energy
  • Thermal energy
  • Light energy
• Kinetic energy


  The energy a body possesses due to its motion
• Gravitational potential energy


  The energy stored in a body due to its height from the ground
• Elastic potential energy


  The energy stored in a body due to its condition such as stretched, compressed or bent
• Chemical potential energy


  The energy that is stored in substances and released through chemical reactions
• Electrical energy


  The energy due to the flow of electric charges (electrons)
• Thermal energy


  The energy stored in a body due to its temperature
• Light energy


  Energy in the form of electromagnetic waves that are visible to the eye
• Work


  The transfer of energy from one object to another or from one form to another
• Work is done when a force is exerted to move an object through a distance in the direction of the force applied
• For work to be done, the object must move in the same direction as the force
• Work is not done when the direction moved by the object is not in the same direction as the force applied, or when the force is applied on the object but the object does not move
• Work done is affected by the size of the force applied and the distance moved by the object in the direction of the force applied
• The law of conservation of energy states that energy cannot be created or destroyed, it can only be converted from one form to another
• Energy is always conserved, meaning the total amount of energy before transformation is the same as after transformation
• Energy sources


  • Renewable
  • Non-renewable
• Biofuels


  The burning of animal or plant matter to produce heat energy and drive turbines for generating electricity
• Geothermal energy


  Heat energy from the Earth obtained by tapping hot rock/hot springs/geysers to produce steam to drive turbines for generating electricity
• Hydroelectric energy


  The energy of water from upland lakes/reservoirs flowing down a hill/mountain to drive water turbines at the bottom, which then generate electricity
• Wind energy


  The kinetic energy of the wind, which can drive turbines to generate electricity
• Solar energy


  Energy from the Sun that can be used with solar panels to generate heat or with solar cells to generate electricity
• Non-renewable energy sources


  • Fossil fuels (coal, natural gas, crude oil)
• Fossil fuels


  Energy sources that take millions of years to form from the remains of plants and animals, and cannot be replenished quickly
• Fossil fuels are widely used in transportation and power plants, but their availability is limited and they are likely to be depleted soon
• An 'energy crisis' is a shortage of energy sources, often due to depletion of fossil fuels
• Ways to conserve energy

  • Turn off lights and electrical equipment when not in use
  • Use energy-efficient appliances
  • Use public transport
  • Recycle materials
  • Develop more efficient engines
• Work done formula


  WD= F× D

  Force (F)

  Distance (D)
• GPE = Mass × Gravitational field strength × Height