5.1 Forces and their Interactions

• Scalar quantity


  • A quantity that only has a magnitude
  • A quantity that isn't direction dependent
• Vector quantity


  A quantity that has both a magnitude and an associated direction
• How a vector quantity can be drawn

  • As an arrow
  • The length of the arrow represents the magnitude
  • The arrow points in the associated direction
• Force


  A push or pull acting on an object due to an interaction with another object
• Categories that all forces can be split into

  • Contact forces (objects touching)
  • Non-contact forces (objects separated)
• Contact forces


  • Friction
  • Air resistance
  • Tension
• Force is a vector quantity
• Vector quantities


  • Velocity
  • Displacement
  • Force
• Weight


  The force that acts on an object due to gravity and the object's mass
• What quantities weight depends on

  • The object's mass
  • The gravitational field strength at the given position in the field
• Unit for weight


  Newton (N)
• Centre of mass


  The single point where an object's weight can be considered to act through
• Equipment to measure weight

  A calibrated spring-balance or newton-meter
• Resultant force


  The single force that is equivalent to all the other forces acting on a given object