Solving for the RPM of a Malfunctioning Motor

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In summary, the conversation discusses the relationship between the rotational speeds of two motors in a machine and the resulting beat frequency heard if they are not operating at the same rpm. The tachometer indicating the rotation rate of one motor is malfunctioning, but it is known that the other motor is running faster. Using the formula w1-w2 = 2pi/T, the rotational speed of the faster motor can be calculated by determining the number of rotations it has completed in the given time period of 21 seconds.
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akan
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Homework Statement


Suppose you're operating a machine with two motors. If the two motors are not operating at the same rpm, you will hear a periodic variation in the intensity of the sound-that is, beats. Suppose the tachometer that indicates the rotation rate of one motor is malfunctioning. The operational one shows 3600 rpm. You hear a beat every 21 s. You are certain the other motor is running fast.

What is its rotational speed in rpm?

Homework Equations


w1-w2 is the frequency of amplitude change (according to the textbook).

3. Attempt at solution
delta_w = 2pi/T = w1-w2
w1 - 2pi/T = w2

w2 is not valid (given that I have converted all units to standard and back into rpm). So I think my formula isn't valid. Can someone derive a correct one please? Thanks.
 
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  • #2
akan said:

Homework Statement


Suppose you're operating a machine with two motors. If the two motors are not operating at the same rpm, you will hear a periodic variation in the intensity of the sound-that is, beats. Suppose the tachometer that indicates the rotation rate of one motor is malfunctioning. The operational one shows 3600 rpm. You hear a beat every 21 s. You are certain the other motor is running fast.

What is its rotational speed in rpm?

Homework Equations


w1-w2 is the frequency of amplitude change (according to the textbook).

3. Attempt at solution
delta_w = 2pi/T = w1-w2
w1 - 2pi/T = w2

w2 is not valid (given that I have converted all units to standard and back into rpm). So I think my formula isn't valid. Can someone derive a correct one please? Thanks.

How many times has one motor turned in 21 seconds?

If during the beat the "faster" one precessed such that you discrened a "beat" wouldn't that mean that the faster one - over that time - rotated 1 more complete time than the other?
 
  • #3
>> How many times has one motor turned in 21 seconds?
The first one rotated 3600 rpm * m/60s * 21s times. I don't know about the second one since it's the one I need to find.

>> If during the beat the "faster" one precessed such that you discerned a "beat" wouldn't that mean that the faster one - over that time - rotated 1 more complete time than the other?

Why would it be "1" more complete time than the other? How do I know how many more times it rotated? How is this tied into the formula? Thanks.
 

FAQ: Solving for the RPM of a Malfunctioning Motor

What is the RPM of a motor?

The RPM (revolutions per minute) of a motor refers to the number of full rotations the motor makes in one minute.

How can I determine the RPM of a malfunctioning motor?

To determine the RPM of a malfunctioning motor, you will need to use a tachometer or a multimeter with a tachometer function. Place the tachometer or multimeter on the motor's shaft or a rotating part of the motor and it will measure the RPM.

Why is it important to solve for the RPM of a malfunctioning motor?

Knowing the RPM of a malfunctioning motor is important because it can help diagnose the issue with the motor. A decrease in RPM may indicate a mechanical problem, while an increase in RPM may indicate an electrical problem.

What factors can affect the RPM of a motor?

The RPM of a motor can be affected by various factors, such as the voltage and current supplied to the motor, the load on the motor, the condition of the motor's bearings, and the type of motor (i.e. AC or DC).

How can I increase the RPM of a malfunctioning motor?

To increase the RPM of a malfunctioning motor, you may need to clean or replace the motor's bearings, adjust the voltage or current supplied to the motor, or troubleshoot and fix any other mechanical or electrical issues with the motor.

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