Question

Twisting couple on a cylinder with mind map
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Answer 1

Answer:

When the two equal or opposite forces are exerted at the two ends of an object, it constitutes a couple. The net force of couple is zero.

The twisting of a structural member about its longitudinal axis by two equal and opposite torques is expressed through a certain angle.  When the disc is rotated on a horizontal plane in order to twist the wire, the different elements of the wire undergo shearing strains.  

The twisting couple per unit twist of the wire is called the torsional rigidity or modulus of torsion of the cylinder of wire.  

Twisting couple per unit twist = C ∅ = - I d² ∅/dt²,

where the Angle of twist at the lower end of the wire is ∅, restoring couple is C∅, where C is the torsional rigidity of the wire, and I is the moment of inertia of the disc about the axis of the wire. the '-' sign indicates that the couple C∅ decreases the twist.