Newton
The newton (symbol: N) is the SI derived unit of force, named after Sir Isaac Newton in recognition of his work on classical mechanics.
[edit] Definition
The newton is the unit of force derived in the SI system; it is equal to the amount of force required to give a mass of one kilogram an acceleration of one meter per second squared . Algebraically:
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[edit] Examples
- 1 N is the force of earth's gravity on an object with a mass of about 102 g (1⁄9.8 kg) (such as a small apple).
- On Earth's surface, a mass of 1 kg exerts a force of approximately 9.81 N [down] (or 1 kgf). The approximation of 1 kg corresponding to 10 N is sometimes used as a rule of thumb in everyday life and in engineering.
- The decanewton (daN) = 10 N is increasingly used when specifying load bearing capacity of items such as ropes and anti-vibration mounts, being approximately equivalent to the more familiar non-SI unit of force, the kgf.
- The force of Earth's gravity on a human being with a mass of 70 kg is approximately 687 N.
- The scalar product of force and distance is energy. Thus, in SI units, a force of 1 N exerted over a distance of 1 m is 1 N·m = 1 joule, the SI unit of energy.
- Because a newton is a small force, it is common to see forces expressed in kilonewtons or kN, where 1 kN = 1 000 N.
- A metric tonne (1 000 kg) exerts a force of 9.8 kN (or 1 000 kgf) under standard gravity conditions on Earth.
Units of force
| | newton
(SI unit) | dyne | kilogram-force,
kilopond | pound-force | poundal
|
| 1 N
| ≡ 1 kg·m/s²
| = 105 dyn
| ≈ 0.10197 kp
| ≈ 0.22481 lbf
| ≈ 7.2330 pdl
|
| 1 dyn
| = 10−5 N
| ≡ 1 g·cm/s²
| ≈ 1.0197×10−6 kp
| ≈ 2.2481×10−6 lbf
| ≈ 7.2330×10−5 pdl
|
| 1 kp
| = 9.80665 N
| = 980665 dyn
| ≡ gn·(1 kg)
| ≈ 2.2046 lbf
| ≈ 70.932 pdl
|
| 1 lbf
| ≈ 4.448222 N
| ≈ 444822 dyn
| ≈ 0.45359 kp
| ≡ gn·(1 lb)
| ≈ 32.174 pdl
|
| 1 pdl
| ≈ 0.138255 N
| ≈ 13825 dyn
| ≈ 0.014098 kp
| ≈ 0.031081 lbf
| ≡ 1 lb·ft/s²
|
| The value of gn as used in the official definition of the kilogram-force is used here for all gravitational units.
|
Three approaches to mass and force units
| System
| Gravitational
| Engineering
| Absolute
|
| Force (F)
| F = m·a
| F = m·a/gc = w·a/g
| F = m·a
|
| Weight (w)
| w = m·g
| w = m·g/gc ≈ m
| w = m·g
|
|
|
| Units
| English | Metric
| English | Metric
| English | Metric
|
| Acceleration (a)
| ft/s2 | m/s2
| ft/s2 | m/s2
| ft/s2 | m/s2
|
| Mass (m)
| slug | hyl
| pound-mass | kilogram
| pound | kilogram
|
| Force (F)
| pound | kilopond
| pound-force | kilopond
| poundal | newton
|
[edit] References
[edit] See also
- Joule, the SI unit of energy, equivalent to 1 newton exerted over a distance of 1 meter.
- Pascal, the SI unit of pressure, equivalent to 1 newton acting on an area of 1 square meter.
- Kilogram-force, the force exerted by Earth's gravity on one kilogram of mass.
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