SI units, force, mass and acceleration

Abstract 

The current Système International (SI) of units comprises seven fundamental or base units, two supplementary units, several derived units and a range of prefixes. The fundamental units are the metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). The supplementary units are the units of plane and solid angles: the radian (rad) and steradian (sr). Derived units are defined by algebraic expressions of the fundamental units, and are given special names for ease of use. Examples include temperature in degrees Celsius (°C), force in newtons (N), pressure in pascals (Pa), energy in joules (J) and power in watts (W). A prefix may be added to an SI unit to concisely express decimal multiples or submultiples. Several non-SI units remain in common use, including pressure in millimetres of mercury (mm Hg) and standard atmospheres (atm), and energy in calories (cal). Force (F), mass (m) and acceleration (a) are linked by Newton’s second law, which states that ‘the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass’, and may be expressed mathematically as F = ma. Mass is a measure of how much material is in an object, but weight is a measure of the gravitational force exerted on that material in a gravitational field. Despite the terms being used interchangeably in everyday usage, these two concepts are not equivalent and have units of kg and N, respectively.

Keywords: acceleration, derived, force, fundamental, mass, SI units, Système International, weight