Answer, and give a reason. Which modulus decides how far a metal shaft twists when a motor turns it?
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.
- Which modulus decides how far a metal shaft twists when a motor turns it?
- For a metal, which is smaller, its shear modulus or its Young's modulus?
- Two plates are held together by a bolt, and the plates are pulled apart along their faces. What kind of stress acts in the bolt?
Need a reminder? The key ideaShow
Shear modulus: , where acts along the face of area , and the angle of shear is . Liquids and gases have no shear modulus.
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) The shear modulus: twisting a shaft makes each thin slice slide round over its neighbour, which is shear.
Step 2. (b) The shear modulus, about a third of : metals are easier to shear than to stretch.
Step 3. (c) Shear stress: the plates try to slide the two halves of the bolt past each other across its section.
Answer: (a) Shear modulus. (b) The shear modulus. (c) Shear.
Watch out. A bolt in a joint like this is designed for its shear strength, not its tensile strength.
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