Torque
Torque is the rotational analogue of linear force.
Torque is the rotational correspondent of linear force, also referred to as the moment of force or simply the moment. It is defined as a twist applied to an object with respect to a chosen axis, such as when a screwdriver applies torque to a screw, causing it to rotate around its axis. The term torque is generally used in physics, while moment is more common in engineering, following the definition used in US physics.
- field
- Physics and mechanics
- known_for
- Rotational correspondent of linear force; moment of force
- SI_unit
- Newton-meter (N⋅m)
- symbol
- Lowercase Greek letter tau (𝜏) or M for moment of force
- etymology
- From Latin torquēre, 'to twist'
Lore & Background
Usage was attested the same year by Silvanus P. Thompson in the first edition of Dynamo-Electric Machinery. Thompson described torque as 'that which produces or tends to produce torsion (around an axis),' arguing it is better to treat this action as a single definite entity rather than using terms like 'couple' and 'moment,' which suggest more complex ideas.
Reader's Guide
Torque is fundamental in physics and mechanics as the rotational counterpart of linear force. It is defined mathematically as the cross product of the displacement vector and the force vector: τ = r × F, with magnitude τ = rF sin θ, where r is the lever arm length, F is the force magnitude, and θ is the angle between them. The direction of torque is given by the right-hand grip rule. Torque determines the rate of change of angular momentum: net torque equals dL/dt. For a point particle, angular momentum L = Iω, where I = mr² is the moment of inertia and ω is the angular velocity. The SI unit is the newton-meter. Understanding torque is essential for analyzing rotational motion in engineering, from simple levers to complex machinery, and its historical terminology reflects a shift from describing forces in terms of couples to a unified concept of twist.
Did You Know?
- The SI unit for torque is the newton-meter (N⋅m).
More in Classical Mechanics 1-21
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