Forces and elasticity

• Elastic materials


  Return to their original length when the forces are removed
• Inelastic materials


  Do not return to their original shape
• Investigating stretching


  1. Use a clamp stand

  2. Measure length without weights

  3. Hang 1N weight and record length

  4. Repeat with 2N weight

  5. Repeat for each weight
• To bend, squash, or stretch an object you always have to apply more than one force
• A material like clay is inelastic because it does not return to its original shape when the forces are removed
• A rubber band is elastic because it does return to its original length
• Limit of proportionality


  The point beyond which a spring does not return to its original length
• Directly proportional


  Doubling the force doubles the extension
• The steel spring gives a straight line through the origin on a graph
• You can calculate the extension of the spring using the equation: extension = new length - original length
• Weights used in the investigation

  • 1N
  • 2N
  • 4N
  • etc.
• When you finish your investigation, you can plot your results on a scatter graph
• Put weight in newtons on the y-axis and extension in mm on the x-axis
• The table shows the results achieved when a student stretched a spring
• Figure 2 shows a graph of how a polythene strip, a rubber band, and a steel spring behave when they are stretched
• The results table includes weights and corresponding lengths and extensions
• To stretch or squash an object you need at least two forces
• When the weight is 2N, the extension of the steel spring can be found from the graph
• When the weight is 4N, the extension of the steel spring can be found from the graph