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Imagine!
Those naughty entertainers describing a 40% radial mark when it is actually
40.4% Disgraceful! As it happens, those fellows also mentioned
other strategies,
such as taking an empty beer can and filling it full; then weighing or
taking volumes (in a sight glass?) to establish quarters. :-)
Brian W
On 2/1/2011 4:16 PM, John Mallinckrodt wrote:
As Bob Sciamanda points out, the balance point is not the same as the half (or quarter) mass point. I find that the balance point is at .424413 R and the half mass point is at .403973 R. About 52.37% of the semicircle mass lies closer to the diameter than the balance point.
John Mallinckrodt
Cal Poly Pomona
On Feb 1, 2011, at 12:24 PM, brian whatcott wrote:
The question:
How can I find the quarter full mark using a dipstick in a [horizontal
axis] cylindrical fuel tank as fitted to a truck?
The answer:
Cut a circle from card.
Draw a diameter, and a perpendicular radius.
Cut a semicircle out on the diameter line.
Balance the semicircle on the radius line with a pencil tip for the pivot.
This is the centroid of the shape, and represents the center of mass of
a similar cylinder - this is about 40% of the radial distance from the
center.
A stick marked with three lines scaled to the diameter of the fuel tank
in question
therefore fits the purpose. A mark at 70% of the diametrical length,
one at 50% of the diameter, and one at 30% of the diameter.
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