EasyPhysicsHigh School (11–12)Mechanics › Elasticity and Mechanical Properties of SolidsConceptualBoard Exam
Answer, and give a reason. Why are rubber pads placed under heavy machines and in shock absorbers? …
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Answer, and give a reason.
- Why are rubber pads placed under heavy machines and in shock absorbers?
- A steel spring and a rubber band are both elastic. Which is more elastic in the physics sense?
- Why does a wire that has been bent back and forth many times break more easily?
Need a reminder? The key ideaShow
Hooke's law: within the proportional limit, stress is in proportion to strain. Past the elastic limit some stretch stays; at the ultimate strength the stress is greatest; the material breaks at the breaking point. A stiff material has a large modulus; a strong one has a large breaking stress.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Each time rubber is squeezed and released, the loop in its stress-strain graph turns some energy into heat. The pads soak up vibration instead of passing it on.
Step 2. (b) Steel: it needs a far larger stress for the same strain, so it opposes deformation more strongly.
Step 3. (c) Elastic fatigue: repeated stress, especially past the elastic limit, weakens the metal until it fails below its normal breaking stress.
Answer: (a) Rubber turns vibration into heat. (b) Steel. (c) Fatigue.
Watch out. 'Stretchy' and 'elastic' are not the same word in physics.
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