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 metre per second squared. Algebraically:
{\rm 1~N = 1~\frac{kg\cdot m}{s^2}}.
Examples
1 N is the force of earth's gravity on an object with a mass of about 102 g ( kg) (such as a small apple).
On Earth's surface, a mass of 1 kg exerts a force of approximately 9.80665 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 dot product of force and distance is mechanical work. Thus, in SI units, a force of 1 N exerted over a distance of 1 m is 1 Nˇm of work. The Work-Energy Theorem states that the work done on a body is equal to the change in energy of the body. 1 Nˇm = 1 J (joule), the SI unit of energy.
It is common to see forces expressed in kilonewtons or kN, where 1 kN = 1 000 N.
A tonne (metric ton)=(1 000 kg) exerts a force of 9.80665 kN (or 1 000 kgf) under standard gravity conditions on Earth.
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