Nate Core Practice Test

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If you double the RPM of a motor, what happens to the CFM?

Decreases
Increases
Stays the same
Triples

The correct answer is: Triples

When you double the RPM (revolutions per minute) of a motor, the CFM (cubic feet per minute) increases in a manner that is proportional to the speed at which the motor operates. This means that as the RPM increases, the volume of air (or fluid) moved per minute also increases. Specifically, if you double the speed, you can expect a significant increase in the flow rate, influenced by how the system is designed and the relationship between motor speed and output flow. In many applications, particularly in fans and blowers, the CFM is related to RPM by a cubic function. Therefore, if you significantly increase the RPM, such as doubling it, the airflow does not merely double; it increases at a rate that could be approximated as tripling, under ideal conditions. This principle reflects the idea that mechanical devices operate more efficiently at higher speeds, leading to enhanced performance metrics such as airflow. In summary, when RPM is doubled, the airflow increases, and in certain contexts, this increase can manifest as a tripling of the CFM, illustrating a strong relationship between speed and output performance in mechanical systems.