Forces

• Force


  Anything that causes an object to move, speed up, slow down, change shape or go in a different direction
• Newton meter


  Unit used to measure force in the laboratory
• Balanced forces


  Forces that cancel each other out, causing no movement or constant velocity
• Unbalanced forces


  Forces that cause an object to accelerate (speed up or slow down)
• Contact forces


  Forces that must be in direct contact with the object they are moving
• Friction


  A contact force that opposes motion
• Lubrication


  Reducing friction by filling gaps between surfaces with oil
• Non-contact forces


  Forces that do not have to touch an object to move it
• Gravity


  A non-contact force that pulls objects towards the centre of a large mass
• Weight


  The force pulling an object towards the centre of the Earth
• Mass


  The amount of matter in an object
• Converting mass to weight

  weight (in newtons) = mass (in kilograms) × 10
• Balanced forces


  • Cancel each other out, causing no movement or constant velocity
• Unbalanced forces


  • Cause an object to accelerate (speed up or slow down)
• Friction allows brakes to be used
• Friction between shoes and ground allows movement
• Friction slows down rain and hailstones
• Friction causes wear and tear of machinery
• Terminal velocity


  The highest speed at which an object will fall through the air before the force of friction balances the force of gravity
• Elastic object


  An object that stretches when force is applied and returns to its original shape when the force is removed
• Elastic limit


  The most an object can be stretched or bent before it cannot return to its original shape or breaks
• Moment of a force

  The turning effect of a force causing an object to spin
• Lever


  A rigid body that is free to move about a fixed point
• Smaller force x larger distance = larger force x smaller distance
• Levers increase the effectiveness of a force, acting as a force amplifier
• Pressure


  The force exerted per unit area
• Work


  Done when a force results in an object moving a distance
• Power


  The rate at which work is done
• Key terms


  • force
  • newton meter
  • balanced forces
  • unbalanced forces
  • contact forces
  • friction
  • lubrication
  • non-contact forces
  • gravity
  • weight
  • terminal velocity
• Hookes Law: The extension of an object is directly proportional to the force acting on it.
• Pressure = Force/ Area
• Pressure unit: n/m² or pascals
• Power = work done/ time taken
• Power unit: Watt/W
• Work = Force × Distance
• Work unit: Jouels/J
• Force = Mass × Acceleration