Physics

• Forces

  Interactions between objects that can change their shape or the way they are moving
• Non-contact (field) forces

  • Gravity, electrostatics, magnetism
• Contact forces

  • Friction, air resistance, tension, normal contact force
• Friction

  A force between two surfaces that impedes motion and may result in heating
• Air resistance

  A form of friction
• Pairs of objects interact to produce a force on each other, which can be represented as vectors
• Scalars

  Quantities that have magnitude only
• Vectors

  Quantities that have direction as well as a magnitude
• Distance, speed and time are examples of scalars and displacement, velocity, acceleration, force and momentum are examples of vectors
• Weight


  The force acting on an object due to gravity
• Elastic distortion


  An object returns to its original shape when the forces are removed
• Inelastic distortion


  An object does not return to its original shape
• Elastic potential energy

  Energy stored in a stretched spring
• Gravitational potential energy


  Energy gained when an object is raised vertically
• Kinetic energy


  Energy of a moving object
• Power


  The rate at which energy is transferred or the rate at which work is done
• When a system changes, energy is transferred
• Simple pendulum

  Example of oscillating motion where energy is transferred between kinetic and gravitational potential energy
• Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed
• Friction and air resistance

  Forces that dissipate energy by heating the surroundings
• Sankey diagram

  Diagram showing how the overall energy in a system is redistributed
• Fuels

  • Useful store of energy, different fuels suitable for different situations
• When a fuel is used, some energy is transferred to the surroundings. Some fuels are more efficient than others
• Renewable energy sources


  • Wave power
  • Solar power
  • Geothermal power
• Wave

  A disturbance caused by an oscillating source that transfers energy and information in the direction of wave travel, without transferring matter
• Transverse wave

  • Oscillations are perpendicular to the direction of energy transfer
• Longitudinal wave

  • Oscillations are parallel to the direction of energy transfer, with areas of compression and rarefaction
• Electromagnetic waves and water waves are transverse, sound waves are longitudinal and mechanical waves may be either transverse or longitudinal
• Wave behaviour

  • Reflection
  • Transmission
  • Absorption
• Wave behaviour

  • Refraction
  • Diffraction
• For appreciable diffraction to take place the wavelength of the wave has to be comparable to the size of the obstacle or gap
• Wave properties

  • Frequency
  • Wavelength
  • Period
  • Amplitude
• Electromagnetic waves and water waves

  • Transverse
• Sound waves

  • Longitudinal
• Mechanical waves


  • May be either transverse or longitudinal
• Waves can

  1. Be reflected

  2. Be transmitted

  3. Be absorbed (or a combination of these) at the boundary between two different materials
• Waves can

  1. Undergo refraction due to a change in velocity

  2. Undergo diffraction through a narrow gap or at an edge
• Students may be required to apply these ideas to the reduction of diffraction in optical instruments, ultrasound waves in medicine and radio wave reception
• Wave motion can be described in terms of

  • Frequency
  • Wavelength
  • Period
  • Amplitude
  • Wavefront
• Relationship between wave speed, v, frequency, f, and wavelength, λ

  v = f × λ