physics

• Energy is not something you can hold in your hand, it's just an idea
• 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


  Different types of energy
• Energy stores


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


  Energy of motion, calculated as 1/2 * mass * velocity^2
• Gravitational potential energy


  Energy an object has due to its position in a gravitational field, calculated as mass * gravitational field strength * height
• Elastic potential energy


  Energy stored in a stretched or compressed spring, calculated as 1/2 * spring constant * extension^2
• Thermal energy


  Energy transferred due to a temperature difference, calculated as mass * specific heat capacity * temperature change
• Chemical potential energy

  Energy stored in chemical bonds, e.g. in food or fuels
• In a closed system, no energy is lost to the surroundings and no energy comes in from the surroundings
• Gravitational potential energy at the top of a roller coaster

  Converted to kinetic energy at the bottom
• Rearranging equations to find unknown values

  1. Divide both sides to isolate the unknown

  2. Square root both sides to remove a square

  3. Substitute known values
• If energy is lost to the surroundings, the system is not closed
• Work


  Another word for energy used
• Specific heat capacity practical

  1. Use an electric heater in a cylinder

  2. Measure power, mass, and temperature change

  3. Use the equation energy = mass * specific heat capacity * temperature change
• Power


  Rate of energy transfer, calculated as energy / time
• Efficiency

  Ratio of useful energy output to total energy input, calculated as useful energy out / total energy in
• Insulation reduces heat loss from buildings
• Energy sources


  Where energy is harnessed from, e.g. fossil fuels, nuclear, renewable sources
• Finite energy sources like fossil fuels and nuclear fuel will eventually run out
• Renewable energy sources like wind, hydroelectric, and solar can be replenished
• Electricity


  Flow of electric charge, transferring energy from a source to a component
• Electric circuit


  Complete loop of components and wires allowing charge to flow
• Potential difference (voltage)


  Amount of energy transferred per unit of charge, measured in volts
• Current


  Rate of flow of electric charge, measured in amperes
• Resistance


  Property of a component that opposes the flow of electric current, measured in ohms
• Ohm's law states that potential difference, current, and resistance are directly proportional
• Resistance of a resistor is constant, but resistance of a bulb changes with current
• PD and current or V and I

  Directly proportional
• Graph of PD and current

  • Straight line
  • Negative values for both but still a straight line through the origin
  • Constant gradient shows a resistor has constant resistance
• Steeper gradient of the line

  Lower the resistance of the resistor
• Ohm's law


  V = I * R (PD in volts = current in amps * resistance in ohms)
• Increasing PD and current for a metal

  Resistance increases
• Reason for change in resistance for a metal

  Metals consist of a lattice of ions surrounded by a sea of delocalized electrons, higher current leads to more collisions between electrons and ions, making it harder for electrons to flow
• Resistors are specially made so their resistance stays constant even if temperature changes
• Diode


  Only lets current flow through in one direction, has very high resistance in one direction and very low resistance in the other
• LED (light emitting diode)


  Acts like a diode but also emits light
• Measuring resistance of a metal wire

  1. Connect wire to circuit with crocodile clips

  2. Measure V and I

  3. Calculate R using Ohm's law

  4. Move one clip to change length of wire and see how resistance changes
• Series circuit


  • Total PD is shared between components
  • Current is the same for all components
  • Total resistance is the sum of all resistances