metre per second
SI coherent derived unit
|metre per second||m s−1||speed,
The metre per second, symbol m s−1, is the SI coherent derived unit of speed (scalar quantity) and velocity (vector quantity).
The fixed numerical value of the speed of light in vacuum, c, is defined as 299 792 458 when expressed in the unit m s−1.
Inverting this relation gives an exact expression for the metre per second in terms of the SI defining constant c :
The effect of this definition is that one metre per second is exactly 1⁄299 792 458 of the speed of light in vacuum.
The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time.
Velocity is a vector quantity; both magnitude and direction are needed to define it.
The speed of an object is the magnitude of its velocity. Speed is a scalar quantity.
Using SI coherent units,
- v is the speed in metres per second, symbol m s-1,
- d is the distance travelled in metres, symbol m,
- t is the travel time in second, symbol s.
At a constant speed, an object travelling a distance of one metre in a time of one second, has a speed of 1 m s-1.