Enigma 1717: On the beach
26 September 2012
Posted by on
From New Scientist #2884, 29th September 2012 [link]
Clearing my attic, I found my old 8mm cine-projector and films of our children. It still worked. The film moves through the projecting gate at an essentially constant speed from the stock spool to an identical take-up spool. The empty spool has a 4-centimetre diameter and the spool when full has a diameter (to the outside of the film) of 12 cm. The playing time is 17 minutes. Each spool has five spokes, so it is easy to compare speeds of rotation. A scene of children playing on the beach started when the ratio of the speed of rotation of the take-up spool to that of the stock spool was 5:3 and ended when it was 3:5.
How long did the scene last?