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Velocity (V) is distance traveled in a given time, usually noted in feet per minute (FPM). Velocity is determined by dividing the distance (feet) traveled by the time (minutes) required to travel that distance.
• Velocity (in ft. per min.) = Distance (in feet) ÷ Time (in minutes)

Important: When referring to gears, velocity usually means pitch line velocity or the velocity of a particular point on the pitch line or circle. Gear speed is usually given in revolutions per minute (RPM), and in each revolution a point on the pitch circle moves a distance equal to the circumference of the pitch circle. The pitch line velocity, then, equals the circumference multiplied by the RPM.

As the circumference is πD inches, then:
• πD ÷ 12 feet, or .262D (feet)
• V = .262D x RPM

Sample Problem: 
Calculate the velocity of a gear with a pitch diameter of 4.5" turning at 800 RPM.
Velocity (V) =.262D x RPM =.262 x 4.5 x 800 =943 FPM