Title: Diameter and distance
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Hi Pat,
Are yo sure that the wheel was not 141.47 mm in
diameter rather than exactly 142? If that were the case, then its
circumference would be 444.44 mm or 4/9 m. Since 4 and 9 are both
integers, a pair of gear wheels can easily be used to "multiply" the number of
revolutions.
Regards
Martin.
----- Original Message -----
Sent: Saturday, January 28, 2006 7:19
AM
Subject: [USMA:35897] Diameter and
distance
Dear
Phil and All,
Recently, I visited a Sunday Market where, amongst a lot
of junk, I found a measuring instrument that I think is called a trundle
wheel. It has a small wheel that is geared to turn a four digit indicator and
it measures in metres.
Four digits means that it can be used to measure
up to 999.9 metres. I tested it over a measured (with a tape) twenty metre
path and it seems to be accurate enough for approximations.
However, I
have a problem. The little wheel that drives this device is exactly 142
millimetres in diameter and I can't figure out out why this value might have
been chosen because the 142 millimetre wheel has a circumference of 446.1
millimetres and this seems to me rather an odd value.
Cab anyone
help?
Cheers,
Pat Naughtin LCAMS (USMA), Member NSAA*
PO Box
305, Belmont, 3216
Geelong, Australia
Phone 61 3 5241
2008
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