SI derived unit m), the SI derived unit of density. The names of SI derived units, when written in full, are in lowercase. However, the symbols for units named after persons are written with an uppercase initial letter. For example, the symbol for hertz is "Hz"; but the symbol for metre is "m". The International System of Units assigns special names to 22 derived units, which includes two dimensionless derived units, the radian (rad) and the steradian (sr). Some other units such as the hour, litre, tonne, bar and electronvolt are not SI units, but are widely used in conjunction with SI units.
Revolutions per minute former measures the angular velocity and the latter reflects the number of revolutions per second. If the non-SI unit rpm is considered a unit of frequency, then . If it instead is considered a unit of angular velocity and the word "revolution" is considered to mean 2 radians, then . Revolutions per minute Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min) is the number of turns in one minute. It is a unit of rotational speed or the frequency of rotation around a fixed axis. According to the International System of Units (SI), rpm is