Loading and Unloading Rubber Band Discussion Points. How can you identify from the loading graph areas where the rubber band was a) easier to stretch and b) harder to stretch. What does the area under the (extension, force) graph represent?
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Loading and Unloading Rubber Band Discussion Points How can you identify from the loading graph areas where the rubber band was a) easier to stretch and b) harder to stretch. What does the area under the (extension, force) graph represent? Why does the unloading curve not follow the same line as the loading curve? Can the shape of the curves be explained in terms of the structure of rubber?
Structure of Rubber See Link http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/make-a-rubber-fridge/
Work done in stretching an Elastic Band • The area underneath a force extension curve represents the work done in stretching the material. • 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 done? • What is the link between hysteresis and formula 1 racing?
Testing the Strength of different materials • Crudely add force to different materials until they break. • Plot a a bar chart of force against material. • Safety – glasses, G clamps, common sense