Re: [Phys-l] real-world problem

[chuck britton <cvbritton@mac.com>]

Neat thing is - that the CarGuys would be glad to hear about these 
calculations.
Somebody might even get a mention on air.

	(Anybody ever seen a fuel gage with better than 5% accuracy?)

The MythBusters are also tuned into outsider comments.

.
At 2:16 PM -0800 2/1/11, 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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