Demos: 1R-01 Hooke’s Law and Young’s Modulus
Incremental loading of a 1-m long #20 copper wire is used to illustrate (a) the region of applicability of Hookes Law, (b) the yield point (modulus of elasticty no longer constant) and (c) the breaking stress (copper wire can be stretched about 20% of its original length before breaking).
Directions: USE CAUTION! FALLING WEIGHTS CAN BE POTENTIALLY DANGEROUS! With the weight holder in place, begin adding weights 1 kg at a time. Stretching of the wire will not be evident at first because with 20-gauge wire 3 m long (A = 0.52 mm2), the stretch produced by 10 N of weight is only 0.5 mm! Eventually, however, the elastic limit will be reached and there will be a noticeable sag in the wire. Continually adding weights eventually makes the wire drop quickly and a few more weights will break it. Near this point you should be alert to the breaking of the wire and have your feet out of the way in case a weight might bounce off the foam rubber pad.
Suggestions for Presentation: This demo is about Youngs modulus as much as it is about Hookes Law.