Topic 9

• 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


  Vector quantity - has both magnitude and direction
• Scalar quantity


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


  A quantity that has both magnitude and direction
• Vector quantities


  • Velocity
  • Displacement
  • Force
• The resultant force has a magnitude of 45N
• How vectors are represented

  • Vector arrows
  • Length indicates magnitude
  • Arrow indicates direction
• Calculating resultant magnitude and direction of forces using a scale drawing

  1. Draw the component forces as scaled arrows, joined tip-to-tail

  2. Draw a line connecting the two open ends

  3. Measure the length of this line and convert into the magnitude

  4. Measure the angle between the resultant line and the vertical/horizontal to find the direction
• Moment


  Alternative name for the turning effect of a force
• Moment of force


  Equation: Moment = Force x Distance

  Units: Moment (Nm), Force (N), Distance (m)
• Distance measurement used when calculating a moment

  The perpendicular distance from the pivot to the line of action of the force
• Equilibrium


  The clockwise moments are equal to the anticlockwise moments
• Levers


  • They increase the perpendicular distance of the force from the pivot, so decrease the force needed to produce the same moment
• Lever example


  • 20N force, 4m distance

  10N force, 2m distance

  The object does not rotate as the clockwise and anticlockwise moments are equal
• How levers decrease force required to lift something

  Levers use a pivot point and the concept of moments to reduce the force. The further you are away from the pivot point, the less force you need to lift the object up.
• Lubricating levers/gears


  Improves efficiency by reducing resistance and energy dissipation (as heat) from frictional forces