Energy

• Energy


  Not something you can hold in your hand, it's just an idea, a number that tells us what will happen when objects interact in a system
• Total energy in any interaction is always conserved, energy cannot be created or destroyed
• Energy can be turned into matter (Mass) but it's still technically true that energy cannot be created or destroyed
• Energy stores


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


  Calculated using e = 1/2 mv^2, the faster an object goes the more kinetic energy it has
• Gravitational potential energy (GPE)


  Calculated using e = mgh, the higher off the ground an object is the more GPE it has available to lose if it falls to the ground
• Elastic potential energy


  Calculated using e = 1/2 kx^2, found in springs
• Thermal energy


  Calculated using e = mc∆T, an increase in thermal energy results in particles moving faster
• Sound and vibrational energy are just kinetic energy of particles moving
• Chemical potential energy


  Found in food and fuels, no equation for it
• Energy transfer


  1. From one object to another

  2. From one store to another store
• In a closed system


  No energy is lost to the surroundings, no energy in from the surroundings
• Gravitational potential energy (GPE) at the top of a roller coaster


  Equals the kinetic energy (KE) at the bottom
• Rearranging equations


  1. Use symbols not words

  2. Move things to the other side by doing the opposite

  3. Cancel out terms that appear on both sides
• If more GPE at the top than KE at the bottom


  Energy must have been lost to the surroundings, so it cannot be a closed system
• Specific heat capacity practical

  1. Use an electric heater, voltmeter, ammeter to measure power

  2. Measure mass and temperature change

  3. Plug into rearranged shc equation
• Power


  The rate of energy transferred, P = E/t, unit is W (J/s)
• Efficiency


  Ratio of useful energy out to total energy in, can be expressed as a decimal or percentage
• Energy sources


  • Finite/non-renewable: fossil fuels, nuclear fuel
  • Renewable: wind, hydroelectric, solar, geothermal, biofuels