Torsion in mechanics is defined as which of the following?

• A. The twisting of an object due to an applied torque.
• B. The bending of a beam under load.
• C. The elongation due to thermal expansion.
• D. The frictional resistance in a joint.

Answer: (A)

Torsion in mechanics refers to twisting of an object that occurs when a torque is applied. When a torque acts, opposing ends tend to rotate relative to each other, causing the material cross-sections to experience shear as they try to rotate about the axis. This twisting is the defining effect of torsion, and it’s characterized by shear stresses that vary with radius from the axis.

The description that matches this is twisting of an object due to an applied torque. The other scenarios describe different deformations: bending from a transverse load causes curvature of a beam; elongation from thermal expansion is a change in length due to temperature rise; frictional resistance in a joint concerns resisting sliding, not twisting from torque.