Math CentralQuandaries & Queries


Question from Bruce, a parent:

a tachometer of a Ford Explorer reads 2,100 rpm at 60 mph. Find the equivalent angular velocity in degrees per minute and radians per minute

Hi Bruce.

An angular speed is just the rate at which the angle is changing. Whether you revolve in revolutions per minute (rpm) or degrees per second or radians per hour, it is all just an angular momentum. Your question therefore is just one of converting units.

The question is this: "What is the conversion factor from rpm to degrees per minute or radians per minute"?

In all cases, you have minutes as the time unit, so you don't need to change anything there.

However, you just need to multiply by the factor you would use to convert revolutions (one complete circle) to degrees or radians.

There are 360 degrees in a circle (revolution) and 2 π radians in a circle.

Hope this helps,
Stephen La Rocque.

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