energy

• Energy Stores


  • Thermal energy stores
  • Kinetic energy stores
  • Gravitational potential energy stores
  • Elastic potential energy stores
  • Chemical energy stores
  • Magnetic energy stores
  • Electrostatic energy stores
  • Nuclear energy stores
• Energy is Transferred Between Stores

  1. Energy is transferred to an object

  2. Energy is issued in one of the object's stores
• Energy is transferred mechanically by a force doing work, electrically (work done by a moving charges), by heating, or by radiation (e.g. light, sound)
• System


  A single object or a group of objects that you're interested in
• When a System Changes, Energy is Transferred


  1. Energy can be transferred into or away from the system

  2. Energy can be transferred between different objects in the system

  3. Energy can be transferred between different types of energy stores (e.g. from the kinetic energy store of an object to its thermal energy store)
• Closed systems


  • Systems where neither matter nor energy can enter or leave
  • The net change in the total energy of a closed system is always zero
• Energy can be Transferred by Heating

  1. Energy is transferred to the water (from the kettle's heating element) by heating into the water's thermal energy store (causing the temperature of the water to rise)

  2. Energy is transferred electrically to the thermal energy store of the kettle's heating element, which transfers energy by heating to the water's thermal energy store
• Work Done


  1. Initial force exerted

  2. Causes energy transfer

  3. From chemical energy store

  4. To kinetic energy store
• Friction between car's brakes and wheels

  1. Does work

  2. Causes energy transfer

  3. From wheels' kinetic energy store

  4. To thermal energy store
• Collision between car and stationary object

  1. Normal contact force does work

  2. Causes energy transfer

  3. From car's kinetic energy store

  4. To other energy stores
• Some energy might also be transferred away by sound waves
• Falling objects


  1. Gravitational force does work

  2. Transfers energy

  3. From gravitational potential energy store

  4. To kinetic energy store
• For a falling object with no air resistance, energy lost from gravitational potential energy store equals energy gained in kinetic energy store
• Air resistance acts against all falling objects and causes some energy to be transferred to thermal energy stores of the object and surroundings
• Materials with high specific heat capacity


  • Need to gain lots of energy in their thermal energy stores to increase in temperature
  • Release a lot of energy when they cool down again
  • Can store a lot of energy
• Specific heat capacity


  The amount of energy needed to raise the temperature of 1 kg of a substance by 1 °C
• Investigating specific heat capacity

  1. Measure the mass of the block

  2. Wrap it in an insulating layer

  3. Insert the thermometer and heater

  4. Measure the initial temperature

  5. Set the potential difference of the power supply to 10 V

  6. Turn on the power supply and start a stopwatch

  7. Measure the temperature increase over time

  8. Turn off the power supply

  9. Calculate the energy transferred and plot a graph

  10. Find the gradient of the straight part of the graph

  11. Specific heat capacity = (gradient x mass of block)
• conservation of energy

  energy can be transferred usefully, stored or dissipated, but can never be created or destroyed
• what is conduction?


  Transfer of heat through direct contact between particles.
• what is convection?


  where energetic particles move away from hotter to cooler regions
• lubrication?


  reduces frictional forces
• insulation?


  reduces the rate of energy transfer by heating
• Investigating the Effectiveness of Different Insulators

  1. Boil water in a kettle

  2. Pour some of the water into a sealable container

  3. Measure the mass of water in the container

  4. Use a thermometer to measure the initial temperature of the water

  5. Seal the container and leave it for five minutes

  6. Remove the lid and measure the final temperature of the water

  7. Pour away the water and allow the container to cool to room temperature

  8. Repeat the experiment, but wrap the container in a different material
• Factors that Affect how Good a Material is at Insulating

  1. Investigate how the thickness of the material affects the temperature change of the water

  2. The thicker the insulating layer, the less energy is transferred and the smaller the temperature change of the water
• non-renewable energy resources? 


  Will run out

  examples - coal, oil, natural gas

  all do damage to environment

  Provide most of our energy
• renewable resources? 


  Will never run out

  Examples- sun(solar), wind, water waves, hydro-electricity, bio-fuel, geothermal, tides

  Less damaging to environment

  Don't provide much energy (unreliable) depending on weather
• bio-fuels 


  made form plants and waste

  PROS:

  -carbon neutrals (if plants growing at the rate of burning them)

  -fairly reliable

  CONS:

  -cost (expensive)

  -loss of natural habitats due to production

  -burning of vegetations increases co2 and methane emissions