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



Yes, approximately. So the ball does show less area at 2 m. Well Hewitt
got it from Bill DeBuvitz, and apparently neither noticed the problem. But
why didn't the editor spot it? I suspect they were trying to make it
simple, and simplified too much.

Unfortunately this type of thing gets passed around by teachers, and the
correction often does not!

John M. Clement
Houston, TX


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


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