# What is *speed*?

**Speed**is a measure of how fast something is moving. The average speed of an object in a certain time is the distance the object travelled divided by the time. Speed is often confused with

*velocity*.

**Velocity**is speed with a direction. In other words, velocity is the vector quantity and speed is the scalar quantity.

## Input

**Millimeters Per Second**is the speed of an object covering a distance of one millimeter in a time of one second.

## Output

**Mach**is the ratio of a speed of an object compared to the speed of sound. For the calculation of this converter, the speed of sound in dry air at mean sea level at standard temperature of 15°C is used, which is 340.3 meters per second.