Unit of acceleration

SI unit of acceleration is meter/second²

In the previous example, we calculated the acceleration of the train as (-12 km/hour)/minute.
 

Look at it carefully.The unit of time appears twice. Remember that acceleration is the rate of change of velocity. The unit of velocity is meter/second and the change in velocity with time gives us unit (meter/second)/second which is the unit of acceleration. That is why the unit of time appears twice.

For example, the train running with the speed of 60 kilometer/hour, stops in 5 minutes, so the rate of velocity change was kilometer/hour/minute. The standard unit of acceleration is meter/second/second, commonly written as meter/second² (read as meter per second square). It means that you measured the velocity in meter/second and time in second.

There are other units of acceleration also: km/s², km/h² etc. One unit can be converted into another with an appropriate conversion factor of respective units.