Equipment typically required (per set):
- Clamp and stand
- Large rubber band
- Slotted masses on hanger
- Graph paper
The rubber band is hung from the clamp stand and two points are marked on the band with the pen. The gap between the two marks will denote the extension value and so one mark should be drawn near the top and one near the bottom of the band.
The mass hanger is hung from the band and an measurement of extension taken. As each slotted mass is added, the extension is observed and plotted on a graph. One by one, the masses can be removed and measurements taken each time.
This practical is very similar to the 'stretching a spring' experiment, however the results will be vastly different.
When stretching a spring, students should find that the extension is directly proportional to the masses added (the graph they plot will have a straight section) This means for example that if 10N is added, the extension may be 2cm, if 20N is added then the extension may be 4cm and so on. This is called 'Hooke's Law' and this principle can be applied to the stretching of wires and metalwork in bridges and architecture.
The mass/extension ratio of a rubber band is different and the results taken should prove that Hooke's Law does not apply.
This practical can be conducted alongside the one involving spring stretching and the results can be compared.