Project motion

Project motion

The trajectory of a ball in lawn bowls
Rod Cross
Physics Department, University of Sydney, Sydney 2006, Australia

͑Received 6 November 1997; accepted 26 January 1998͒
The main objective in lawn bowls is to bowl a ball along a curved trajectory on a smooth grass
surface so that it stops closer to the jack ͑a small white ball͒ than the opponent’s ball. The curvature
of the path is induced by shaping the ball so that one side is heavier than the other. Some of the
properties of the trajectory are described to illustrate this interesting example of precessional
motion. © 1998 American Association of Physics Teachers.

Lawn bowls is a popular outdoor sport for both men and
women, especially with more senior citizens, since the game
does not require a particularly high level of physical fitness.
The game is played at a leisurely pace on an immaculately
manicured lawn and requires only an empirical knowledge of
the laws of precession. Because the ball is weighted on one
side, it travels in a curved path whose radius of curvature
decreases with time until the ball eventually stops. The ball
has a mass typically of about 1.5 kg, and a diameter of about

Am. J. Phys. 66 ͑8͒, August 1998

12 cm, with small variations allowed to suit the individual
bowler and the playing surface conditions. The ball is
launched with a speed of about 4 msϪ1, at an angle of about
10° to the direct line of sight to the desired end point, then
rolls at a walking pace for about 14 s over a total distance of
about 25 m.
A weighted ball precesses like a gyroscope or a spinning
top1,2 but its axis of rotation is not anchored to a fixed point.
As a result, the precessional motion is combined with linear
motion to generate a curved trajectory. In this respect, the
path of the ball is similar to that of a wheel or a coin3,4 that
© 1998 American Association of Physics Teachers


rolls along a surface of its own accord. As the ball or the...

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