physics unit 1: energy

a system is an object or group of objects.

kinetic energy = 0.5 x mass x speed squared. or Ek=1/2mv2

gravitational potential energy = mass x gravitational field strength x height. or Ep=mgh

elastic potential energy = 0.5 x spring constant x extension squared. or Ee=1/2ke2

specific heat capacity.

internal energy is the total kinetic and potential energy of all the particles that make up a system. doing work on a system increases the energy stored in a system. heating changes the energy stored in a system by increasing he energy of particles within it. as the energy increases this will either increase the temperature or produce a chnage of state. if the temperature increases the increase depends on:

  • the mass of the substance heated.
  • what the substance is
  • the energy input.

specific heat capacity of a substance is the amount of energy required t raise the temperature of one kilogram of the substance by one degree Celsius.

change in thermal energy = mass x specific heat capacity x temperature change. or △E=mc△θ

required practical

  1. set up the apperatus.
  2. measure the start temperature.
  3. switch on the electric heater for one min.
  4. measure the end temperature
  5. measure the voltage and current to find the power
  6. repeat for different liquids.
    7.calculate the specific heat capacity.

independent variable: type of liquid
dependant: the temperature.
Control variables: amount of liquid used and energy provided.

energy transfers.

energy can be transferred usefully stored or dissipated. in a closed system total energy never changes but is still transferred from one store to another.

e.g when an electricity powered lift raises the carriage: - it transfers electrical energy into gravitational potential energy.

  • some energy is dissipated into the surroundings as heat and vibrational (sound) energy.

unwanted transfers reduce by:

  • lubrication: reduces the friction that produces heat.
  • tightening any loose parts: prevents unwanted vibration that wastes energy as sound
  • thermal insulation: reduces heat loss.

required practical

  1. take four test tubes and wrap each one with a different type of insulation
  2. fill each test tube with hot water and measure the start temperature of each one.
  3. start the stopwatch and record the temperature every minute for 10 minutes.
  4. plot the results on a graph of time against temperature.

independent: type of insulation. dependant: temperature. control variables: times at which temperature is measured, volume of water in each test tube, and thickness of insulating material.

national and global energy resources.

biofuel - renewable - transport and EG - large areas of land required for growing fuel crops. at expense of food crops in poorer countries.
wind - renewable - EG - not a constant source of energy. can be noisy and dangerous to birds, some say they ruin aesthetic of countryside.
hydroelectric - EG - large areas of land to be flooded, altering ecosystems and displacing people that live there.
geothermal - EG and heating - available in limited places where not rocks can be found near surface e.g Iceland .
tidal - EG - variation in tides affect output. have a high initial cost, alter habitats and cause problems for shipping.
Solar - EG and some heating - depends on light intensity. none at night. high cost in relation to power output.
Nuclear - EG and some military transport - produces radioactive waste but no other emissions. costly. reliable output
coal - EG heating, some transport - produces greenhouse gases and contributes to acid rain. reliable output.
Oil - transport and heating - reliable. burning produces CO2 NO2 and SO2.
Gas - EG heating, some transport - reliable. CO2 but not SO2