Fig 1How the ball moves1–7 · ↑↓ km/h · T tiltoutswing · 108 km/h · side force 0.30 g
The ball's path, its shadow and a plumb line; sideways movement drawn 5× larger, read in true cm on the board behind the stumpsSame release with no swing or spin forces (the plain rider on the board)Lens: the ball seen from behind the machine, 48× larger: seam and stitches, and the spin axis as an arrow (right-hand rule) with a curl showing the turnA two-wheel bowling machine sets the ball's spin axis with the angle of its axles and launches it down an instrumented lane toward the stumps; the lens shows the ball as a camera behind the machine sees it, about 48× larger. For a seam-up quick the seam stays upright, angled about 20° and steadied by about 11 rev/s of backspin, and the ball is pushed toward where the seam points: the side force in the wind tunnel began at about 15 m/s (54 km/h), peaked at about 0.3 of the ball's weight near 30 m/s (108 km/h) and was gone for a new ball at about 129 km/h. Above about 129–137 km/h with a new ball, or from about 105 km/h with a ball 100 overs old, it reverses and swings against the seam (R. D. Mehta 2000, 2006). The model drives the ball with those forces, so at 108 km/h it swings 28 cm (1.3°) by a 6 m length; that is the wind-tunnel peak, and ten elite and pathway Australian fast bowlers averaged 0.80° outswing and 0.58° inswing, about 10–13 cm at a 6 m length (Lindsay and colleagues 2025). Spinners' balls drift and dip through the Magnus force and turn off the pitch: off-spinners averaged 25.0 rev/s with the seam about 62° toward leg, leg-spinners 29.3 rev/s at about 47° toward off, both at about 67 km/h (Beach and colleagues 2014). The flight and the lens play 10× slower than life. Illustrative, not from the guides: the 71.5 mm, 156 g ball, air density, drag and lift coefficients, the force curves' shape between the quoted speeds, release height, the spinners' 4 m length, the bounce, the spin axis's 12° tilt (which sets the drift; T flips it) and the googly's seam direction. On the lane the ball is drawn about 5× its size, its centre raised so it sits on the strip as it pitches. The swing in the readout is measured at the bounce, 6 m from the stumps; the board behind the stumps reads the sideways line where the ball is now, in true centimetres at the drawn scale, with the stumps' 22.86 cm width marked on it. Each light curtain's beams light as the ball cuts them, and a mark stays on the path where it did. The creases are 1.22 m in front of each set of stumps, which are 20.12 m apart.
Stance Cricket™Stance Lab · Ball