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How to Convert RPMs to Velocity

Revolutions per minute (rpm) describes the frequency at which something revolves in a circular path. For example, an object revolving at 20 rpm completes 20 revolutions in 60 seconds. The velocity of the object depends on the rpm and the distance traveled during each revolution. Objects following the circumference of a large circle have to travel further than objects following the circumference of a smaller circle, even though they revolve at the same rate.

Instructions

- 1
  Measure the distance from the object to the point about which the object revolves. This value is the radius of the circle followed by the object. For example, to determine the velocity of the tip of the arm in a centrifuge, measure the distance from the center of the centrifuge to the end of the arm.
- 2
  Use the formula for the circumference of a circle to determine the length of each revolution. The equation is circumference = pi x radius^2, (Reference 2) where pi = 3.1415. For example:
  
  a radius of 2 feet gives a circumference of 12.566 feet -- 3.1415 x 2 x 2 = 12.566
- 3
  Multiply the value from Step 2 by the number of revolutions per minute. The result is the total distance traveled in one minute. For example:
  
  12.566 x 30 rpm = 12.566 x 30, or 376.98
  
  The result is the velocity measured in feet per minute. In the example, the velocity is 376.98 feet per minute.

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