Torque

Torque or moment of force is a concept in Physics that describes the rotational force of an object. It is a measure of the force that can cause an object to rotate about an axis. Torque is a vector quantity, meaning it has both a direction and a magnitude.

Definition

The mathematical definition of torque is the cross product of the lever-arm distance and force, which tends to produce rotation. Mathematically, Torque (τ) is defined as:

τ = r x F

where:

• r is the distance from the axis of rotation to the point where the force is applied
• F is the force applied
• x denotes the cross product

Units

In the International System of Units (SI), the unit of torque is the newton metre (N⋅m). This is not to be confused with the unit newton metre per second (N⋅m/s), which is a unit of work.

Static equilibrium

For an object to be in static equilibrium, not only must the sum of the forces be zero, but also the sum of the torques (moments) about any point. For a two-dimensional situation with horizontal and vertical forces, the sum of the forces requirement is two equations: ΣH = 0 and ΣV = 0, and the torque a third equation: Στ = 0. That is, to solve statically determinate equilibrium problems in two-dimensions, three equations are used.

See also

• Force
• Lever arm
• Moment (physics)
• Newton metre
• Static equilibrium

References

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