6 - Stretching a spring

• Investigating the relationship between force and extension for a spring - Setting up apparatus:

  1. We have a clamp stand, two bosses and two clamps.
  2. Place a heavy weight on the clamp stand to stop it falling over
  3. Attach a metre rule and a spring
  4. Ensure the top of the spring is at the zero point on the meter rule and that the meter rule is vertical
  5. Place a wooden splint onto the bottom of the spring as a pointer
  6. Ensure the pointer is horizontal or the readings will be inaccurate

  A) bosses

  B) clamps

  C) clamp stand

  D) heavy weight

  E) meter rule

  F) pointer

  G) spring

  
• Investigating the relationship between force and extension for a spring - experiment:

  1. Read the position of the pointer on the meter rule
  2. Hang a 1N weight on the spring
  3. Read the new position of the pointer on the meter rule
  4. Continue adding 1N weights to the spring and reading the position of the pointer

  A) 1N weight

  B) pointer

  
• Investigating the relationship between force and extension for a spring - calculation and graph:

  1. Work out the extension produced by adding each weight
  2. To do that, subtract the length of the unstretched spring from each reading
  3. Plot the results on a graph with the Weight on the X axis and Extension in newtons (N) on the Y axis in metres (m)

  In this practical, we are meant to use the spring to work out the weight of a mystery object e.g. a stone. To do this, we need to measure the extension of the spring when the stone is hanging from it and then we read the weight of the stone.

  
• The graph is a straight line going through the origin, therefore meaning that the extension is directly proportional to the weight. The graph also shows that the spring is elastic because if we remove the weight, then the extension returns to 0.

  
• If we repeated the experiment using a rubber band, we would achieve a more curved line

  
• In the experiment testing a stone, if we were to add too much weight to the spring, then we get a straight line graph with a curve at the end because we have overstretched the spring i.e. if we took all the weight away, the spring would still show an extension. This is called inelastic deformation as by overstretching the spring, we have exceeded the limit of proportionality