The newton (symbol: N) is the unit of force in the International System of Units (SI). It is defined as 1 kg⋅m/s, 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 Newton's second law of motion.
A newton is defined as 1 kg⋅m/s (it is a derived unit which is 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, 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. The newton thus became the standard unit of force in the Système international d'unités (SI), or International System of Units.
In more formal terms, Newton's second law of motion states that the force exerted on an object is directly proportional to the acceleration hence acquired by that object, thus:
represents the mass
of the object undergoing an acceleration
. As a result, the newton
may be defined in terms of the kilogram (
), and second
At average gravity on Earth (conventionally, ), a kilogram mass exerts a force of about 9.8 newtons. An average-sized apple exerts about one newton of force at Earth's surface, which we measure as the apple's weight on Earth.
- 1 N = 0.10197 kg × 9.80665 m/s2 ().
The weight of an average adult exerts a force of about 608 N.
- 608 N = 62 kg × 9.80665 m/s2 (where 62 kg is the world average adult mass).
It is common to see forces 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.
- 1 kN = 102 kg × 9.81 m/s2.
So for example, a platform that shows it is rated at will safely support a load.
Specifications in kilonewtons are common in safety specifications for:
the holding values of fasteners, , and other items used in the Construction industry;
working loads in tension and in Shear stress;
thrust of , and ;
clamping forces of the various moulds in injection-moulding machines used to manufacture plastic parts.