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Re: [Phys-l] Figuring Physics in the March TPT The Physics Teacher



bc dimmer than usual, he hopes.

p.s. the sun and moon subtend ~ 1/2 deg. [~ 8.7 miliradian] So the ball has a 23 cm D?




On 2009, Feb 18, , at 21:13, John Clement wrote:

You will see the same fraction of the basketball as the moon if the ball is
about 26m away from the observer, assuming I did the calculation right. The
absolute distance is not the important parameter, rather the subtended angle
or the ratio of size/distance are the important variables. The almost
parallel comment would also apply to a basketball at 26m. But the rays are
not parallel. A grape at 2 m beats the moon for the fraction of area you
can see with one eye.

While the reverse perspective comment is valid, it is probably not a good
way to visualize how a magnifying glass makes more area visible.

And notice the problem changes if you use 2 eyes rather than 1. For small
objects the visible area increases as you bring it closer if you use 2 eyes.
The answer is correct, but with wrong reasoning.

John M. Clement
Houston, TX


OK, I give up; what's wrong w/ the basket ball and moon problem.

bc evidently almost dead.


On 2009, Feb 18, , at 13:50, John Clement wrote:

It has part of the analysis of the problem wrong. Can anyone spot it!

John M. Clement
Houston, TX