Tor"sion (?), n. [F., fr. LL. torsio,
fr. L. torquere, tortum, to twist. See Torture.]
1. The act of turning or twisting, or the state of
being twisted; the twisting or wrenching of a body by the exertion of a
lateral force tending to turn one end or part of it about a longitudinal
axis, while the other is held fast or turned in the opposite
direction.
2. (Mech.) That force with which a thread,
wire, or rod of any material, returns, or tends to return, to a state of
rest after it has been twisted; torsibility.
Angle of torsion (of a curve) (Geom.), the
indefinitely small angle between two consecutive osculating planes of a
curve of double curvature. -- Moment of torsion
(Mech.) the moment of a pair of equal and opposite couples which
tend to twist a body. -- Torsion balance
(Physics.), an instrument for estimating very minute forces, as
electric or magnetic attractions and repulsions, by the torsion of a very
slender wire or fiber having at its lower extremity a horizontal bar or
needle, upon which the forces act. -- Torsion scale,
a scale for weighing in which the fulcra of the levers or beams are
strained wires or strips acting by torsion.