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Propeller Music comprises a set of six propellers, sized between 60 and 90 cm in diameter, mounted horizontally upon axles approximately 2 cm above the level of the floor. These propellers are entirely mechanical and visitors are invited to spin propellers as they desire. Propellers are mounted using low friction sealed bearings so they will continue to spin for several minutes after having been pushed. Up to 64 small sensor widget discs, each approximately 5 cm in diameter and 1.5 cm in height, can be arranged underneath the paths of any of the propellers. If a propeller passes over a sensor a sound gesture is triggered, the precise sonic nature of which is dependent upon the speed of the propeller and the accumulation of repeated triggerings (as the propeller spins). If lines of sensors are arranged underneath propellers, musical phrases can be formed according to the visitor's desires. As a propeller spins it will repeat this phrase, gradually slower and slower, until friction and air resistance force the propeller to a standstill. Multiple coincident patterns are formed by employing more than one propeller simultaneously. Each propeller will probably express a different tempo, and will decay and cease at a different rate. It is this juxtaposition of multiple and independent patterns, with a clear visual cause and display of progress, that is the crucial mechanism of the piece.