Newton (unit)

Definition

One newton is the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in direction of the applied force.

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 le Système International d'Unités (SI), or International System of Units.

This SI unit is named after Isaac Newton. As with every International System of Units (SI) unit named for a person, the first letter of its symbol is upper case (N). However, when an SI unit is spelled out in English, it should always begin with a lower case letter (newton)—except in a situation where any word in that position would be capitalized, such as at the beginning of a sentence or in material using title case. Note that "degree Celsius" conforms to this rule because the "d" is lowercase.— Based on The International System of Units, section 5.2.

Newton's second law of motion states that F = ma, where F is the force applied, m is the mass of the object receiving the force, and a is the acceleration of the object. The newton is therefore:

where the following symbols are used for the units: N for newton, kg for kilogram, m for metre, and s for second.

In dimensional analysis:

F = M L T 2

where F is force, M is mass, L is length and T is time.

Examples

At average gravity on earth, (conventionally 7000980665000000000♠g = 9.80665 m/s²), a kilogram mass exerts a force of about 9.8 newtons. An average-sized apple exerts about one newton of force, which we measure as the apple's weight.

1 N = 0.102 kg × 9.80665 m/s²    (6999102000000000000♠0.102 kg = 102 g)

The weight of an average adult exerts a force of about 550 – 800 N.

566 N = 57.7 kg (average Asian adult weight) × 9.80665 m/s²791 N = 80.7 kg (average North American adult weight) × 9.80665 m/s²

Commonly seen as kilonewtons

It is common to see forces expressed in kilonewtons (kN) where 1 kN = 1000 N. For example, the tractive effort of a Class Y steam train and the thrust of an F100 fighter jet engine are both around 130 kN.

One kilonewton, 1 kN, is 102.0 kgf, or about 100 kg of load.

1 kN = 102 kg × 9.81 m/s²   

So for example, a platform rated at 321 kilonewtons (72,000 lb_f) will safely support a 32,100 kilograms (70,800 lb) load.

Specifications in kilonewtons are common in safety specifications for:

the holding values of fasteners, Earth anchors, and more, in the building industry.

working loads in tension and in shear.

rock climbing equipment.

thrust of rocket engines and launch vehicles

clamping forces of the various moulds in injection moulding machines used to manufacture plastic parts.