springs and moments

• Experiment to see how adding masses to a spring causes it to stretch


  • Set up apparatus as shown in diagram
  • Measure mass of each mass and calculate weight (force applied)
  • Do a pilot experiment first to check masses are good size
  • Measure natural length of spring
  • Add mass, allow to rest, measure new length, calculate extension
  • Repeat until enough measurements (at least 6)
  • Plot force-extension graph
• If the line of best fit is a straight line, there is a linear relationship between force and extension (they're directly proportional)
• When the line begins to bend, the relationship is now non-linear between force and extension - the spring stretches more for each unit increase in force
• Spring constant


  Gradient of the straight line on the force-extension graph
• Elastic potential energy


  Energy stored in a stretched spring, equal to 1/2 * spring constant * extension^2
• Moment of a force

  The turning effect of a force, given by force * perpendicular distance from pivot to line of action of force
• If the total anticlockwise moment equals the total clockwise moment about a pivot, the object is balanced and won't turn
• Levers


  • Increase the distance from the pivot at which force is applied, so less force is needed to get the same moment
  • Make it easier to do work, move a load or turn a nut
• Gears


  • Circular discs with teeth that interlock
  • Turning one causes another to turn, in the opposite direction
  • Transmit the rotational effect of a force from one place to another
  • 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, as the distance to the pivot is greater