Question

Problem 1.9
A wire of length 1m and diameter 1mm is
clamped at one of its ends. Calculate the couple
required to twist the other and by 90°. Rigidity
modulus = 2.8 ×10^10Pa​

Answer 1

in mechanics, a couple is a system of forces with a resultant moment but no resultant force. A better term is force couple or pure moment. Its effect is to create rotation without translation, or more generally without any acceleration of the centre of mass.