Forces

• Vector


  A quantity that has magnitude and direction. E.g. force, velocity, displacement
• Scalar


  A quantity that has magnitude and no direction. E.g. speed, distance, mass
• Force


  A push or a pull on an object that is caused by it interacting with something
• Contact forces


  • Friction
  • Air resistance
  • Tension
• Non-contact forces


  • Magnetism
  • Gravitational force
• Weight calculation

  Weight (N) = Mass (kg) x Gravitational Field Strength (N/kg)
• Mass

  The amount of matter (same everywhere)
• Weight

  The force due to gravity
• Resultant force

  The overall force on a point or object
• Newton's First Law of Motion

  • An object will remain stationary or moving constantly unless acted upon by a force
• Equilibrium


  An object has balanced forces
• Elastic deformation


  Goes back to original length after the force has been removed
• Inelastic deformation


  Does not go back to original length after the force has been removed
• Plastic material


  A material that does not go back to its original shape
• Hooke's Law

  The extension of a spring is directly proportional to the force applied, as long as the limit of proportionality is not exceeded
• Limit of proportionality

  The point at which further extension causes inelastic deformation
• Hooke's Law formula

  F = ke

  Force (N) = Spring Constant (N/m) x Extension (m)
• Moment

  The turning effect of a force
• Moment calculation

  M = Fd

  Moment of a force (Nm) = Force (N) x Distance (m)
• Levers

  • Increase the distance from the pivot at which the force is applied, meaning less force is needed to get the same moment
• Gears

  • Different sized gears can be used to change the moment of the force. A force transmitted to a larger gear will cause a bigger moment and the distance to the pivot is greater. The larger gear will turn slower than the smaller gear.
• Pressure calculation

  Pressure=FA
• Increasing the depth in a fluid

  Increases the pressure because at deeper points there is a greater weight of fluid above the object pressing down creating more pressure
• Pressure in a fluid

  p=hρg

  Pressure (Pa) = depth (m) x density (kg/m3) x gravitational field strength (N/kg)
• What is the resultant force?

  A) 600N