A crank is an arm
attached at right angles to a rotating shaft by which reciprocating motion is imparted to or
received from the shaft. It is used to convert circularmotion into reciprocating motion, or vice versa. The arm may be a bent
portion of the shaft, or a separate arm or disk attached to it. Attached to the
end of the crank by a pivot is a rod, usually called a connectingrod. The end of the rod attached to the crank moves in a circular motion,
while the other end is usually constrained to move in a linear sliding
motion.
The term often refers to a
human-powered crank which is used to manually turn an axle, as in a bicycle crankset or
a brace and bit drill. In this case a person's arm
or leg serves as the connecting rod, applying reciprocating force to the crank.
There is usually a bar perpendicular to the other end of the arm, often with a
freely rotatable handle or pedal attached.
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