# 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.

## 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:

${\rm 1~N = 1~\frac{kg\cdot m}{s^2}}.$

## Examples

• 1 N is the force of earth's gravity on an object with a mass of about 102 g (​19.8 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.

## References

• Halliday, Resnick and Walker Fundamentals of Physics, John Wiley & Sons ISBN 0471470619