page_title: Bowling ball
section_title: Ball motion
hierarchical_section_title: Bowling ball / Ten-pin balls / Ball motion
caption_attribution_description: English: Diagram showing skid, hook and roll phases of a bowling ball's path down the lane. Horizontal scale is compressed
context_page_description: A bowling ball is a hard spherical ball used to knock down bowling pins in the sport of bowling.
  Balls used in ten-pin bowling typically have holes for two fingers and the thumb. Balls used in five-pin bowling, candlepin bowling, duckpin bowling, and kegel have no holes, and are small enough to be held in the palm of the hand.
context_section_description: Ball motion is commonly broken down into sequential skid, hook, and roll phases. As the ball travels down the lane in the skid and hook phases, frictional contact with the lane causes the ball's forward (translational) speed to continually decrease, but to continually increase its rev rate (rotational speed). Especially as the ball encounters greater friction in the last ≈20 feet (approximate) of the lane, the ball's axis rotation (side rotation) causes the ball to hook away from its original direction. Concurrently, lane friction continually decreases the angle of axis rotation until it exactly matches the direction of the ball's forward motion, and rev rate (rotational speed) increases until it exactly matches the ball's forward speed: full traction is achieved and the ball enters the roll phase in which forward speed continues to decrease.
  Release ratio denotes the ratio of the ball's forward (translational) speed to its rev rate (rotational speed) at time of release. This ratio continually decreases throughout the ball's travel until it reaches exactly 1.0 when full traction is achieved upon entering the roll phase. A too-high release ratio (a speed-dominant release) causes the ball to reach the pins while still in the hook phase (resulting in a shallow angle of entry that permits ball deflection and resultant leaves of the 10-pin), and a too-low release ratio (a rev-dominant release) causes the ball to enter the roll phase before reaching the pins (sacrificing power to friction that would ideally be delivered to the pins to enhance pin scatter). Ball speed and rev rate are said to be matched if the ball enters the roll phase immediately before impacting the pins, maximizing power imparted to the pins yet helping to provide an entry angle that minimizes ball deflection.
caption: The skid, hook and roll phases of ball motion.
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