Torque
Rotational force that generates or opposes a turning motion — expressed in Newton-meters (Nm) and defined as the product of force and lever arm.
Definition
Torque (symbol M) is a physical quantity that describes how strongly a force generates or resists rotation about an axis. It is the product of the acting force F and the lever arm r – the perpendicular distance between the line of action of the force and the axis of rotation. The SI unit is Newton-meters (Nm). A torque of 1 Nm is produced when a force of 1 N acts at a distance of 1 m from the axis of rotation.
In drive technology, torque is often calculated from motor power and speed. It is the basis for sizing all torque-transmitting components such as shafts, couplings, gearboxes, and fastening elements. The continuous torque of a motor is called rated torque, and the maximum torque before stalling is called breakdown torque — both parameters define the performance limit of the drive.
Formulas
M = Torque in Nm
F = Force in N
r = Lever arm in m – perpendicular distance between the line of action of the force and the axis of rotation
If the force acts at an angle, only its perpendicular component counts: M = F · l · sin α (l = distance from the axis to the point of application, α = angle between the force and this line). From the power and speed of a drive: M = 9550 · P / n with M in Nm, P in kW and n in rpm.
Direction and Force Couple
Torque has a direction: it acts about the axis of rotation and is represented as a vector along that axis. The right-hand rule tells you where it points: if the fingers of your right hand curl in the direction of rotation, your thumb points in the direction of the torque. In drive technology, the direction of rotation (clockwise or counter-clockwise) and the magnitude in Nm are usually sufficient.
A force couple consists of two equal, opposite forces acting in parallel at a distance a – for example two hands on a steering wheel. The forces cancel each other out. A pure couple therefore does not accelerate a body in a straight line; it only sets it rotating. Its moment M = F · a is the same wherever the pivot lies. A shaft coupling ideally transmits exactly this kind of pure torque; radial forces on the bearings arise, for example, from gear meshing, belt tension or shaft misalignment.
Practical Relevance
Torque is the most important parameter when selecting electric motors, gearboxes, and couplings. Under-sized components cannot transmit the required torque and will fail prematurely. Use our torque calculator to quickly determine the required torque for your application.
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