Newton-Meter
The Newton-meter (N·m) is a unit of torque, also known as moment of force, in the International System of Units (SI). It represents the torque produced when a force of one newton is applied perpendicularly to a one-meter moment arm, which is the distance from the axis of rotation to the line of force. The Newton-meter can also be used to measure work or energy, as it is quantitatively equivalent to the joule (J)—the standard unit of energy. Both units express the energy expended when a newton of force is applied over a distance of one meter.
Additionally, the newton-meter relates to the work-energy theorem, which states that the total work done on an object equals the change in its kinetic energy. This principle outlines how applied force affects an object's speed, with positive work increasing speed and negative work decreasing it. In practical applications, devices like spring balances are used as Newton meters to measure force by determining how much a spring stretches under applied pressure. Thus, the newton-meter is essential in various scientific and engineering contexts, providing a tangible understanding of force, torque, and energy dynamics.
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Subject Terms
Newton-Meter
FIELDS OF STUDY: Classical Mechanics
ABSTRACT: This article describes the newton-meter, an International System of Units (SI) unit used to measure torque or energy. It also discusses the Newton meter, a device that measures applied force. The measurement of torque and energy is essential when discussing work, rotational dynamics, and kinetic energy, among other important concepts in the field of classical mechanics.
Principal Terms
- dyne: a unit of force in the centimeter-gram-second (CGS) unit system, equal to 10−5 newtons, or 10 micronewtons.
- energy: the capacity of a system to do work.
- joule: the derived SI unit of work, energy, or heat, equal to the energy expended by applying one newton of force over a distance of one meter.
- moment: the combination of a physical quantity, such as force, and the distance of that quantity from a given reference point.
- Newton meter: a device used to measure force; also called a "force meter" or a "force gauge."
- torque: a moment that measures the ability of a force to rotate an object about an axis; also called "moment of force."
- work: the displacement of an object by the application of force.
- work-energy theorem: the principle that the work performed on an object is equal to the change in that object’s kinetic energy.
Torque
In the metric system, or International System of Units (SI), the newton-meter (N·m) is a unit of torque, also called moment of force. One newton-meter is equal to the torque generated when one newton of force is applied perpendicularly to a one-meter moment arm. A "moment arm" is the distance between the line of force (the point at which force is applied) and the axis of rotation (the point about which the object will rotate).
The newton-meter can be converted to a number of other units. These include the joule (J), which is equal to 1 N·m, and the dyne-centimeter (dyn·cm), which is equal to 10−7 N·m. The joule is also an SI unit. The dyne-centimeter belongs to the centimeter-gram-second (CGS) system of units, which is another variation on the metric system. The dyne is the CGS unit of force.
Energy
The newton-meter can also be used to measure work or energy. In this case, the "meter" part of "newton-meter" refers to the displacement of an object due to the application of force. However, the official SI unit of energy is the joule, defined as the amount of energy used when one newton of force is applied over a distance of one meter.
Quantitatively, the newton-meter and the joule are equivalent. That is why newton-meters can be used to measure energy as well. Both are derived SI units, meaning that they can be expressed in terms of the seven base SI units (meter, kilogram, second, ampere, kelvin, candela, and mole). Thus, both one newton-meter and one joule are equal to the product of one kilogram and one square meter, divided by one second squared:
N·m = J = (kg × m2) / s2
The work-energy theorem relates work to kinetic energy and, by extension, to speed. This theorem states that the total work done on an object—that is, the net force applied—is equal to the change in that object’s kinetic energy. Generally, when the total work is positive, the object’s speed increases, and when it is negative, the object’s speed decreases.
Force
Two classic examples of the use of torque are children on a seesaw and a mechanic using a wrench to turn a lug nut. In both examples, less force is required when it is applied farther from the pivot point or axis of rotation.
The Newton meter, or force meter, is a device that measures force. One type of Newton meter is a spring balance. It works by measuring how much a spring stretches when a force is applied.
Bibliography
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"What Are Forces?" BBC Bitesize. BBC, n.d. Web. 3 Apr. 2015.