On the beach
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?
WIN £15 will be awarded to the sender of the first correct answer opened on Wednesday 31 October. The Editor’s decision is final. Please send entries to Enigma 1717, Â鶹´«Ã½, Lacon House, 84 Theobald’s Road, London WC1X 8NS, or to enigma@newscientist.com (please include your postal address).
Answer to 1711 Illuminated artwork: A cycle takes 4 days and 15 minutes
The winner David Barley of Gillingham, Kent, UK
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