Definitions

• Scalar quantity

  A quantity that has magnitude (size) only
• Vector quantity

  A quantity that has magnitude and direction
• Speed

  Distance travelled per unit time
• Acceleration


  Change in velocity per unit time
• Velocity

  Speed in a given direction
• Average speed


  Total distance / Total time
• Free-fall

  An object moving only under the influence of the earth's gravity
• Acceleration of free fall (g)

  Approximately constant at 9.8m/s2 near the Earth's surface
• Mass

  Measure of the quantity of matter in an object at rest relative to the observer
• Weight

  Gravitational force on an object that has mass
• Gravitational field strength


  Force per unit mass
• Density


  Mass per unit volume
• Spring constant

  Force per unit extension. Formula: k=F/x
• Limit of proportionality

  Point beyond which the spring crosses its elastic limit and becomes permanently deformed
• Newton's second law

  F = ma, where F is net force, m is mass, and a is acceleration
• Circular motion

  Movement of an object along the circumference of a circle or rotation along a circular path
• Solid friction


  Force between two surfaces that may impede motion and produce heating
• Drag force


  Force acting opposite to the relative motion of an object moving through a fluid (liquid or gas)
• Moment of a force

  Measure of the turning effect of a force. Formula: moment = force × perpendicular distance from the pivot
• Principle of moments


  For an object in equilibrium, clockwise moments are equal to anticlockwise moments
• Centre of gravity


  Point at which the weight of a body or system is supposed to be concentrated. In uniform gravity it is the same as the centre of mass
• Momentum

  Mass × velocity. Formula: p = mv
• Impulse

  Force × change in time. SI unit: Newton-second (Ns)
• Principle of conservation of momentum

  When 2 or more bodies interact (collide) in an isolated system, the total momentum stays the same
• Resultant force

  Change in momentum per unit time. Unit: Newtons (N)
• Kinetic energy

  Energy possessed by an object due to its motion
• Gravitational potential energy

  Energy of an object in a gravitational field relative to its position. Formula: mgh
• Chemical energy

  Energy stored in the bonds of chemical compounds
• Elastic (Strain) energy

  Energy stored in an object due to its deformation
• Electrostatic energy

  Potential energy of a system of separated electric charges
• Internal (Thermal) energy

  Energy associated with the random, disordered motion of molecules
• Principle of conservation of energy

  Energy can never be created nor destroyed, it can only be converted from one form to another
• Work

  Force × displacement in the direction of the force. Unit: Joule
• One Joule

  Work done by a force of 1 Newton when it displaces a body through 1m in the direction of the force
• Solar cells (Photovoltaic cells)

  Cells that convert light energy to electrical energy through the photovoltaic effect
• Solar panels (Photovoltaic/Solar-electric panels)

  Panels consisting of many solar cells, designed to absorb the sun's rays for generating electricity or heating
• Wind energy

  Energy of naturally flowing air used to generate electricity
• Renewable energy resources


  Energy from easily replenished sources like the sun and wind
• Non-renewable energy


  Energy from resources that are not easily replenished, like fossil fuels
• Percentage Efficiency


  {Useful energy/Total energy} x 100 or {Useful power/Total power} x 100