Loading and Unloading Rubber Band Discussion Points

Loading and Unloading Rubber Band
Discussion Points
1. How can you identify from
the loading graph areas
where the rubber band was
a) easier to stretch and b)
harder to stretch.
2. What does the area under
the (extension, force) graph
3. Why does the unloading
curve not follow the same
line as the loading curve?
4. Can the shape of the curves
be explained in terms of the
structure of rubber?
Structure of Rubber
See Link
Work done in stretching an Elastic
• The area underneath a force
extension curve represents the
work done in stretching the
• For an elastic band the work
done in loading is greater than
the work done in unloading.
• It is clear from the force curve
that the rubber band does not
obey Hooke's Law. The force
curve for a rubber band is said to
be a hysteresis loop, and the area
between the two curves
represents lost energy.
• Some of the work done on the
rubber band is against internal
friction, which increases the
temperature of the rubber band
and its surroundings.
Discussion Questions
• What is the equation to calculate work done?
• What are the two possible units for work
• What is the link between hysteresis and
formula 1 racing?
Testing the Strength of different
• Crudely add force to different materials until
they break.
• Plot a a bar chart of force against material.
• Safety – glasses, G clamps, common sense