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2010-02-11 9:50 pm

Two wires of the same material but of different lengths and diameters are joined end-to-end and hung vertically and support a load. Which of the following quantities are the same for both wires: tensile force, tensile stress, strain, extension?

The same wires are now hung vertically side-by-side with their ends joined together. Which of the following quantities are now the same: tensile force, tensile stress, strain, extension?

回答 (1)

天同

2010-02-11 11:09 pm

✔ 最佳答案

First case:
1. tensile force: at equilibrium, the tensile forces on the two wires are the same.
2. stress: stress = force/cross-sectional area, since the cross-ectional area is not the same for both wires, hence stresses are not the same.
3. strain: strain = stress/Young's modulus, since Young's modulus is the same for both wires, hence strains are not the same because stresses not the same.
4. extension: extension = strain x natural length, since natural lengths for the two wires are not the same, extensions not the same.

Second case:
since the wires are joined in parallel, the extensions of the two wires must be the same. Hence, following with the arguments as in the first case, strain, stress and tensiles forces are not the same.

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