6: Stretching a Spring

Forces and Elasticity

• A clamp stand

• 2 bosses

• 2 clamps

• Place a heavy weight onto the clamp stand to stop it from falling over.

• Attach a metre rule and a spring.

• The top of the spring must be at the zero point on the metre rule.

• The metre rule must be vertical or else the readings will be inaccurate.

• The bottom of the spring has a wooden splint attached as a pointer.

• This pointer must be horizontal or the readings will be inaccurate.

• We now read the position of this pointer on the metre rule.

• This is the unstretched length of the spring (the length with no force attached)

• We hang a 1N weight on the spring

• We now read the new position of the pointer on the metre rule

• We continue adding 1N weights to the spring and reading the position of the pointer.

• We now need to work out the extension produced by adding each weight.

• Subtract the length of the unstretched spring from each reading.

When a graph starts to curve off, we have overstretched the spring. This exceeds the limit of proportionality.

If we took all the weight away, the spring would still show an extension - inelastic deformation

The spring constant will be the same for any part of the graph as long as it hasn’t exceeded the limit of proportionality.