Newton-metre

Newton-metre (Nm) is the SI unit of torque (also called "moment" in the physical sciences). It is a compound unit composed of the basic SI unit of force, the newton (N), and the SI unit of distance, the metre (m). The Newton-metre measures the amount of rotational force, or torque, applied to an object which causes it to rotate around an axis. In mathematical terms, one Newton-metre is defined as the torque resulting from a force of one newton applied perpendicularly to a moment arm which is one metre long.

Definition

The Newton-metre is a measure of torque (also called "moment"). Torque is a concept in physics that describes the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Mathematically, torque is defined as the cross product of the lever-arm distance and force, which tends to produce rotational motion. In equation form, torque (\(\tau\)) is defined as:

\[\tau = r \times F\]

where:

• \(r\) is the distance from the axis of rotation to the point where the force is applied (in metres),
• \(F\) is the magnitude of the force applied (in newtons),
• \(\times\) denotes the cross product, which means the torque is in the direction perpendicular to the plane formed by the direction of the force and the lever arm.

Units

The unit of torque in the International System of Units is the Newton-metre (Nm). It is important to note that despite its name, the Newton-metre is not a unit of energy or work, even though it is dimensionally equivalent to the Joule, which is the SI unit of energy. The distinction lies in their physical concepts: while energy is a scalar quantity representing the capacity to do work, torque is a vector quantity representing the rotational effect of a force.

Applications

Torque is a fundamental concept in many fields of physics and engineering, especially in the study of mechanics. It is crucial in the design and function of many mechanical systems, including engines, gearboxes, and any system where rotational motion is present. For example, in automotive engineering, the torque output of an engine is a key parameter that determines its performance. In the field of structural engineering, understanding the torques applied to structural elements is essential for ensuring their stability and integrity.

Measurement

Torque can be measured using a variety of tools, such as torque wrenches, which are commonly used in mechanical engineering and automotive repair to ensure that bolts and nuts are tightened to the correct specification. More sophisticated tools, like torque sensors and dynamometers, are used in research and development to accurately measure the torque output of engines and motors.

See also

• Force
• Lever
• Moment of inertia
• Rotational motion
• Statics