The newton (symbol: N) is the unit of force in the International System of Units (SI). It is defined as , the force which gives a mass of 1 kilogram an acceleration of 1 metre per second per second. It is named after Isaac Newton in recognition of his work on classical mechanics, specifically his second law of motion.
A newton is defined as
(it is a named derived unit defined in terms of the SI base units).
One newton is, therefore, the force needed to Acceleration
of mass at the rate of one metre per second squared in the direction of the applied force.
The units "metre per second squared" can be understood as measuring a rate of change in velocity per unit of time, i.e. an increase in velocity by 1 metre per second every second.
In 1946, the Conférence Générale des Poids et Mesures (CGPM) Resolution 2 standardized the unit of force in the MKS system of units to be the amount needed to accelerate 1 kilogram of mass at the rate of 1 metre per second squared. In 1948, the 9th CGPM Resolution 7 adopted the name newton for this force.
The MKS system then became the blueprint for today's SI system of units. (1977
, U.S. Department of Commerce, National Bureau of Standards.
. ISBN 9789282220450
The newton thus became the standard unit of force in the Système international d'unités (SI), or International System of Units.
The connection to Newton comes from Newton's second law of motion, which states that the force exerted on an object is directly proportional to the acceleration hence acquired by that object, thus:
where represents the mass of the object undergoing an acceleration . When using the SI unit of mass, the kilogram (), and SI units for distance metre (), and time, second () we arrive at the SI definition of the newton:
At average gravity on Earth (conventionally,
), a kilogram mass exerts a force of about 9.8 newtons.
An average-sized apple at 200 exerts about two newtons of force at Earth's surface, which we measure as the apple's weight on Earth.
An average adult exerts a force of about 608 N on Earth.
- (where 62 kg is the world average adult mass).
Large forces may be expressed in kilonewtons (kN), where . For example, the tractive effort
of a Class Y steam train locomotive and the thrust
of an F100 jet engine are both around 130 kN.
One kilonewton, 1 kN, is equivalent to , or about 100 kg of load under Earth gravity.
So, for example, a platform that shows it is rated at will safely support a load.