Experts in advanced refrigeration and air-conditioning


What is RPM? Meaning

The RPM unit is very often used when talking about engines and their operation. However, in some cases it can give rise to ambiguity in both its use and definition. Some important information has therefore been given below in order to understand the full scope of the concept.

What does RPM mean?

RPM stands for “revolutions per minute”. This unit expresses the number of times a body turns around its axis in a given time: one minute. The term “revolution” does therefore correspond to the colloquial term of “turns” per minute However, although the RPM unit is a widely used and widespread unit, it is not an official unit in the International System of Measurement. In this system, the Hertz is used to measure this parameter.

Hertz actually measure what are called cycles, which are precisely the number of revolutions per minute that a rotating body makes around an axis. Regardless of whether it is Hertz or RPM, these measurements are widely used when measuring the rotational speed of a body in an engine. It is therefore a measurement widely used in cars and motors in general (as in a condenser, for example). More revolutions per minute always means more power. The power output of an engine is regulated by the gearbox. The device used to measure RPM is called a tachometer.

How to convert rpm into rad/s

As explained above, RPM refers to revolutions per minute. This term is used to express the angular velocity of a rotating system, which can be an engine or a wheel. However, from a mathematical point of view, it is necessary to convert this unit into radians. One radian is the angle subtended at the centre of a circle by an arc that is equal in length to the radius. This means that one revolution along a circle is 2 pi radians, the value of pi being 3.14.

It is essential to take this into account when converting RPM to rad/s (radians per second). The radians equivalent to RPM per second must be calculated first, and then the radians travelling in a given time interval must be obtained. This operation is essential, as the radian per second (rad/s) is the International System unit for measuring angular velocity. As mentioned above, RPM is not a unit of the International System, although angular velocity can also be expressed in these terms. In accordance with the above, the formula thus requires a change from revolutions per minute to radians per second:

1 rpm = 2∏/60 rad/s

By substituting the corresponding values, it is easily possible to switch from one unit to another.

Areacademy, winner of the Industry Initiative of the Year award by ACR News Awards