moments, levers and gears

• Moment


  The turning effect of a force
• Moments


  • Act about a point in a clockwise or anticlockwise direction
  • The point chosen could be any point on the object, but the pivot - also known as the fulcrum - is usually chosen
• Moment of a force

  Calculated using the equation: moment = force x distance
• Moment (M) is measured in newton-metres (Nm), force (F) is measured in newtons (N), and distance (d) is measured in metres (m)
• The distance (d) is the perpendicular distance from the pivot to the line of action of the force
• Moment


  A turning effect of a force
• Pivot


  A point around which something can rotate or turn
• If an object is balanced, the total clockwise moment about a pivot is equal to the total anticlockwise moment about that pivot
• Balanced objects


  • A ball at the bottom of a trough
  • A balanced see-saw
• Calculating for a balanced object

  1. Size of a force

  2. Perpendicular distance of a force from the pivot
• Child's moment = force x distance

  Parent's moment = child's moment
• Rearranging formula to find distance for parent


  d = M/F
• Calculated distance for parent is 0.8 m
• Lever


  A simple machine consisting of a pivot, effort and load
• Pivot


  A point around which something can rotate or turn
• Effort


  Force used to move a load over a distance
• Load


  The overall force that is exerted, usually by a mass or object, on a surface
• Arrangement of lever components

  • Effort - pivot - load
  • Pivot - load - effort
  • Pivot - effort - load
• Effort - pivot - load

  • see-saw, crowbar, scissors
• Pivot - load - effort


  • wheelbarrow, nutcracker
• Pivot - effort - load


  • tweezers, cooking tongs
• Simple levers and rotation

  • Solid beam laid across a pivot, effort applied to rotate one end about the pivot, opposite end also rotates about pivot in same direction, rotates or lifts the load
• Force multiplier


  Something that increases the effect of a force
• The longer the lever, and the further the effort acts from the pivot, the greater the force on the load will be
• Gears


  Toothed wheels used with other gears to turn axles at different speeds
• Axle


  A bar, rod or shaft which passes through a wheel or gear. The wheel or gear will rotate around the axle.
• Rotation and transmission of forces by gears

  1. One gear turns, the other gear must also turn

  2. Where the gears meet, the teeth must both move in the same direction

  3. The gears rotate in opposite directions
• Gears


  • If the driven gear is made larger, it will rotate more slowly but with a greater moment
  • If the driven gear is made smaller, it will rotate more quickly but with a smaller moment
• Gear ratios


  • Low gear ratio on a bike or car
  • High gear ratio on a bike or car
• Calculating gear moments


  1. Find the force on the teeth of the smaller gear

  2. Use the force to calculate the moment of the larger gear
• Turning a gear that has double the radius doubles the turning effect - it is a 2x force multiplier