Definitions

• Energy


  The ability to do work
• Work

  Done when a force moves an object through a distance
• Power


  • 1. The rate at which work is done
  • 2. The rate at which energy is converted from one form into another
• Newton's laws of motion

  • (i) A body will continue in a state of rest or of uniform velocity unless an unbalanced external force acts upon it.

  (ii) The rate of change of a body's momentum is proportional to the force that causes it and takes place in the direction of that force. (F=ma)

  (iii) If body A exerts a force on body B, then body B exerts an equal but opposite force on body A.
• Force


  Anything that causes or tends to cause an acceleration
• Momentum


  The product of a body's mass and velocity
• Friction


  A force that tends to oppose motion
• The principle of conservation of momentum states that in any interaction between bodies, the total momentum before the interaction will equal the total momentum after the interaction, provided no external forces act upon the bodies
• Centripetal acceleration


  The acceleration of a body in circular motion, directed towards the centre of the circle
• Centripetal force


  The force on a body in circular motion, directed towards the centre of the circle
• Newton's law of gravitation


  The force of attraction between any two point masses is directly proportional to the product of the masses, and inversely proportional to the square of the distance between them
• Simple harmonic motion

  Any motion where the acceleration (a) of a particle is proportional to its distance (s) from an equilibrium position
• Hooke's law


  The restoring force on a spring is proportional to the extension of the spring
• Density


  Mass per unit volume
• Pressure


  Force per unit area, measured in Pascal (Pa)
• Boyle's law

  At constant temperature, the pressure on a fixed mass of gas is inversely proportional to its volume
• Archimedes' principle


  A body immersed in a fluid will experience an upthrust equal to the weight of fluid it has displaced
• Law of flotation


  When a body floats it is displacing exactly its own weight of fluid
• Conditions for equilibrium


  • The sum of the forces in any direction equals the sum of the forces in the opposite direction.

  2. The sum of the moments about any point is zero.
• Laws of reflection


  • The angle of incidence equals the angle of reflection.

  2. The incident ray, the normal at the point of incidence, and the reflected ray are all in the same plane.
• Laws of refraction


  • The incident ray, the normal at the point of incidence, and the refracted ray are all in the same plane.

  2. For any pair of media, the sin of i, the angle of incidence, is proportional to the sin of r, the angle of refraction, i.e. sin i/sin r = constant (Snell's law).
• Real image


  Formed by the actual intersection of light rays, can be formed on a screen
• Virtual image


  Formed by the apparent intersection of light rays, cannot be formed on a screen
• Refractive index


  The ratio of the sine of the angle of incidence to the sine of the angle of refraction when light travels from a vacuum into that medium
• Critical angle


  The angle of incidence for which the corresponding angle of refraction is 90°
• Total internal reflection


  Occurs when the angle of incidence in a dense material is greater than the critical angle, light is reflected at the meeting of the two materials
• Wave


  A means of transferring energy through a medium, without any net movement of that medium
• Transverse wave


  The movement of the particles is perpendicular to the movement of the wave
• Longitudinal wave


  The movement of the particles is parallel to the movement of the wave
• Diffraction


  The ability of a wave to spread out after meeting an obstacle or passing through a small gap
• Interference


  Occurs when two waves meet, the total displacement will be equal to the algebraic sum of the individual displacements
• Coherent waves


  Two or more waves that have the same frequency and wavelength, and that are in phase or maintain a constant phase difference
• Polarisation

  The restriction of a wave to vibrations in one plane
• Standing wave


  Produced when two waves of the same frequency and wavelength meet, moving in opposite directions
• Harmonics


  Multiples of the natural frequency of vibration of a body
• Resonance


  The transfer of energy between two bodies of the same natural frequency
• Intensity of sound

  The rate at which energy is crossing a unit area perpendicular to the direction in which the sound is travelling, measured in Bels or decibels (dB)
• Threshold of hearing


  The lowest sound intensity to which an average human ear can respond, 10-12 Wm2 at 1 KHz
• Frequency limits of audibility

  The highest and lowest frequency sound waves that the average human can hear
• Doppler effect


  The apparent change in the frequency of a wave due to the relative motion of the source of the wave or an observer