Physics 2

• Types of energy


  • Chemical energy
  • Kinetic energy
  • Gravitational energy
  • Elastic energy
  • Nuclear energy
  • Thermal energy
  • Magnetic energy
  • Electrostatic energy
• Chemical energy


  Energy stored in chemical bonds, e.g. food, batteries
• Kinetic energy


  Energy of moving objects
• Gravitational energy


  Energy of objects at height
• Elastic energy


  Energy stored when an object is stretched, squashed or twisted
• Nuclear energy


  Energy released in nuclear reactions, e.g. nuclear fission
• Thermal energy


  Energy associated with heat
• Magnetic energy


  Energy stored when like poles are pushed together or unlike poles are pulled apart
• Electrostatic energy


  Energy stored when like charges are moved closer together or unlike charges are pulled further apart
• Calculating power


  1. Convert mass to kg

  2. Use weight = mass x gravity

  3. Use work done = force x distance

  4. Use power = work done / time
• Calculating gravitational potential energy


  1. Use GPE = mass x gravity x height

  2. First calculate mass from weight = mass x gravity
• Calculating work done


  Use work done = force x distance
• Calculating kinetic energy


  1. Use KE = 1/2 x mass x velocity^2

  2. Rearrange to solve for velocity
• Electrical appliances are designed to transfer electrical energy to either thermal energy or kinetic energy
• Energy is conserved


  Energy cannot be created or destroyed, it is simply converted from one form to another
• A Sankey diagram shows the flow of energy, with the width of the arrows representing the relative amounts
• Calculating efficiency


  Use efficiency = useful energy out / total energy in x 100
• Resultant force


  A single force that has the effect of all the forces acting on an object
• Determining resultant force using a diagram

  1. Identify the individual forces and their directions

  2. Add or subtract the forces to find the resultant force
• Determining resultant force using a parallelogram

  1. Draw the individual forces to scale on a diagram

  2. Complete the parallelogram to find the resultant force
• Parallelogram


  Shape with two parallel sides
• Finding resultant force


  1. Draw line from origin of forces

  2. Measure length of line

  3. Measure angle
• Resultant force


  Force represented by line from origin of forces
• Moment


  Force x perpendicular distance from pivot
• Work done = Force x Distance
• Gravitational potential energy lost when suitcase falls over
• Calculating force to start raising suitcase

  1. Clockwise moment = Weight x Distance

  2. Anticlockwise moment = Force x Distance

  3. Solve for Force
• Gear system


  • Small cog to large cog = low speed, high torque
  • Large cog to small cog = high speed, low torque
• Calculating moment on gear wheels

  1. Moment = Force x Radius

  2. Calculate moment on 10 mm wheel

  3. Calculate moment on 30 mm wheel
• Atom has a nucleus with protons and neutrons, surrounded by electron shells
• Electrical components


  • Cell
  • Battery
  • Lamp/Bulb
  • Resistor
  • Variable resistor
  • Thermistor
  • Diode
  • LED
  • Ammeter
  • Voltmeter
  • Fuse
• Voltmeter


  Measures voltage, connected in parallel
• Ammeter


  Measures current, connected in series
• As temperature increases


  Resistance of wire increases
• As temperature increases


  Resistance of thermistor decreases
• Resistance


  Increases with increased temperature in a wire
• Thermistors


  As temperature increases, resistance decreases
• Light dependent resistor (LDR)


  As light levels increase, resistance decreases
• Ohm's law


  The current through a resistor at constant temperature is directly proportional to the potential difference across the resistor
• Components that obey/do not obey Ohm's law

  • Wire (obeys)
  • Filament bulb (does not obey)
  • Diode (does not obey)