**metre per second**

##### SI coherent derived unit

Name | Symbol | Derived quantity | ||

metre per second | m s^{−1} |
speed, velocity |
||

## DefinitionThe metre per second, symbol m s |

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.

### Velocity

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.

### Speed

The speed of an object is the magnitude of its velocity. Speed is a scalar quantity.

Using SI coherent units,

where:

*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}.