# For number of revolutions

as number of revolutions or revolution frequency n or circulation speed f one calls the quotient, in an educated manner from the number of the circulation or revolutions as counter and the time interval t needed for it denominator. The number of revolutions is not of the dimension 1 (“dimensionless”), like it thoseEnding - number to assume leaves, it is thus no number, but physical dimension with the dimension 1/Zeit.

The reciprocal value of the number of revolutions results in the duration of a circulation [itex] T< /math> :

[itex] T= \ frac {1} {n} = \ frac {1} {f}< /math>

Under the angle of rotation [itex] \ varphi< /math> one understands the product of the number of circulation N ina certain time interval and the angle of a circulation (with a circulation [itex] = 2 \ pi [/itex]): [itex] \ varphi = 2 \ pi N< /math>

Over the definition of the angular speed [itex] \ omega = \ frac {\ varphi} {t}< /math> and the values for a revolution one receives the rotative frequency (angular velocity) [itex] \ to omega< /math> too:

[itex] \ omega= {2 \ pi \ cdot n} = {2 \ pi \ f cdot} = \ frac {2 \ pi} {T}< /math> , with the unit [itex] [\ omega] = \ frac {1} {s} = \ mathrm {cycles per second} [/itex] (Hertz).

## unit

SI-UNIT: [itex] [n] = [f] = \ frac {1} {s} = \ mathrm {cycles per second}< /math> (Hertz). The special name Hertz for the reciprocal second should not preferably forNumbers of revolutions to be used.

From other legal time units further “ legal units in the measurement” can be formed for numbers of revolutions,

for example: 1 cycles per second = 1 /s = 60/(60 s) = 60/min = 3600/(60 min) = 3600/h = (24 x 3600)/(24 h) = 86400/d.

Those is not standardfurther frequently indication of numbers of revolutions used in revolutions per minute (rpm), because “revolution” or “U” is not unit; in the English linguistic usage RPM is to be found or r/min.

## examples

of numbers of revolutions in the unit min -1:

• Globe: approx. 0.000694
• records forLanguage course and. A.: 16
• LP records with 25 cm or 30 cm diameters: about 33
• single record with 17 cm diameters: 45
• shellac records: 78
• marine propellers: 70-150
• main rotor of a helicopter: to 400
• autoengines with no-load operation: approx. 700 to 900 (crankshaft)
• floppy disk drives, depending upon type: to approx. 800