The 'metre' (or 'meter') 'per second squared' is the
SI derived unit of
acceleration. It can be either a
scalar or a
vector, depending on whether it is derived from distance or displacement. The
unit is written in symbols as m/s
2, m·s
−2, or m s
−2. It may be better understood when phrased as "
metre per second per
second"—in other words, the increase in speed (in
metres per
second) that is achieved each second; however, it is inappropriate to write the unit as m/s/s.
The SI derived unit of force, the
newton, is equal to one
kilogram metre per second squared, meaning that a force of one newton is needed to give an acceleration of one metre per second squared to a mass of one kilogram. This is an illustration of Newton's second law (see
Newton's laws of motion) in its simplest form, where acceleration is defined as the rate of change of velocity; this means that the metre per second squared is the same unit as the 'newton per kilogram'.