Frequency is used to describe oscillatory motion. It describes the time it takes for a motion to repeat itself. It is measured in hertz, which is one oscillation per second. The frequency of the voltage in North American buildings is usually 60 hertz, which means it oscillates 60 times a second.

Rpm is short for revolutions per minute, and it denotes circular motion, or the rotations completed by an object around an axis. An electrical signal is not converted to rpm, but it can cause a motor to rotate. The motor's frequency can be converted to rpm, and vice versa.

- Skill level:
- Moderate

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## Instructions

- 1
Obtain a problem where the frequency of a motor needs to be converted to rpm. An example is a motor that rotates at 40 hertz. This means that it does 40 complete revolutions per second, or 40/s. Rev is always not explicitly written because it is not a unit.

- 2
Convert hertz from seconds to minutes. One hertz is equal to 60 revolutions per minute, since 1 Hz = 1/s = (1/s)(60 s/min) = 60 rev/min.

- 3
Apply the method in Step 2. Do this by multiplying the frequency by 60. Plugging in the numbers yields 40 hertz = 40 Hz x (60 s/min) = 2400 rev/min = 2400rpm.

- 4
Use the method in Step 2 to convert rpm to hertz. Do this by dividing a given rpm by 60, in order to convert minutes to seconds.

- 5
Practice Step 4 by converting 5400rpm to hertz. The answer is 90 Hz. This is because 5400rpm = (5400 rev/min) (1 min/60 s) = 5400 rev/60 s = 90/s = 90 hertz.