The newton (symbol: N) is the International System of Units (SI) derived unit of force. It is defined as 1 kg⋅m/s^{2}, 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.
newton | |
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General information | |
Unit system | SI derived unit |
Unit of | Force |
Symbol | N |
Named after | Sir Isaac Newton |
Conversions | |
1 N in ... | ... is equal to ... |
SI base units | 1 kg⋅m⋅s^{−2} |
CGS units | 10^{5} dyn |
Imperial units | 0.224809 lbf |
A newton is defined as 1 kg⋅m/s^{2} (it is a derived unit which is defined in terms of the SI base units).^{[1]} One newton is therefore the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in the direction of the applied force.^{[2]} The units "metre per second squared" can be understood as a change in velocity per time, i.e. an increase of 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.^{[3]} 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.
The newton is named after Isaac Newton. As with every SI unit named for a person, its symbol starts with an upper case letter (N), but when written in full it follows the rules for capitalisation of a common noun; i.e., "newton" becomes capitalised at the beginning of a sentence and in titles, but is otherwise in lower case.
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, namely:^{[4]}
where represents the mass of the object undergoing an acceleration . As a result, the newton may be defined in terms of kilograms ( ), metres ( ), and seconds ( ) as
At average gravity on Earth (conventionally, g = 9.80665 m/s^{2}), 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.^{[5]}
The weight of an average adult exerts a force of about 608 N.
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 locomotive and the thrust of an F100 jet engine are both around 130 kN.
One kilonewton, 1 kN, is equivalent to 102.0 kgf, or about 100 kg of load under Earth gravity.
So for example, a platform that shows it is rated at 321 kilonewtons (72,000 lb_{f}) will safely support a 32,100-kilogram (70,800 lb) load.
Specifications in kilonewtons are common in safety specifications for:
newton (SI unit) |
dyne | kilogram-force, kilopond |
pound-force | poundal | |
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1 N | ≡ 1 kg⋅m/s^{2} | = 10^{5} dyn | ≈ 0.10197 kp | ≈ 0.22481 lbf | ≈ 7.2330 pdl |
1 dyn | = 10^{–5} N | ≡ 1 g⋅cm/s^{2} | ≈ 1.0197×10^{−6} kp | ≈ 2.2481×10^{−6} lbf | ≈ 7.2330×10^{−5} pdl |
1 kp | = 9.80665 N | = 980665 dyn | ≡ g_{n} × 1 kg | ≈ 2.2046 lbf | ≈ 70.932 pdl |
1 lbf | ≈ 4.448222 N | ≈ 444822 dyn | ≈ 0.45359 kp | ≡ g_{n} × 1 lb | ≈ 32.174 pdl |
1 pdl | ≈ 0.138255 N | ≈ 13825 dyn | ≈ 0.014098 kp | ≈ 0.031081 lbf | ≡ 1 lb⋅ft/s^{2} |
The value of g_{n} as used in the official definition of the kilogram-force is used here for all gravitational units. |
Base | Force | Weight | Mass | |||||
---|---|---|---|---|---|---|---|---|
2nd law of motion | m = F/a | F = W ⋅ a/g | F = m ⋅ a | |||||
System | BG | GM | EE | M | AE | CGS | MTS | SI |
Acceleration (a) | ft/s^{2} | m/s^{2} | ft/s^{2} | m/s^{2} | ft/s^{2} | Gal | m/s^{2} | m/s^{2} |
Mass (m) | slug | hyl | pound-mass | kilogram | pound | gram | tonne | kilogram |
Force (F), weight (W) |
pound | kilopond | pound-force | kilopond | poundal | dyne | sthène | newton |
Pressure (p) | pound per square inch | technical atmosphere | pound-force per square inch | standard atmosphere | poundal per square foot | barye | pieze | pascal |
Prefix name | N/A | deca- | hecto- | kilo- | mega- | giga- | tera- | peta- | exa- | zetta- | yotta- |
---|---|---|---|---|---|---|---|---|---|---|---|
Prefix symbol | da- | h- | k- | M- | G- | T- | P- | E- | Z- | Y- | |
Factor | 10^{0} | 10^{1} | 10^{2} | 10^{3} | 10^{6} | 10^{9} | 10^{12} | 10^{15} | 10^{18} | 10^{21} | 10^{24} |
Prefix name | N/A | deci- | centi- | milli- | micro- | nano- | pico- | femto- | atto- | zepto- | yocto- |
---|---|---|---|---|---|---|---|---|---|---|---|
Prefix symbol | d- | c- | m- | μ- | n- | p- | f- | a- | z- | y- | |
Factor | 10^{0} | 10^{–1} | 10^{–2} | 10^{–3} | 10^{–6} | 10^{–9} | 10^{–12} | 10^{–15} | 10^{–18} | 10^{–21} | 10^{–24} |