Re: Quiz

"Martin Hogbin" <goatREMOVETHIS123@xxxxxxxxxx> wrote in message
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"Simple Simon" <me@xxxxxxxxxxxxxxxxxx> wrote in message
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According to the solution *** for MIT's OpenCourseWare Physics 8.003,
October 2006 Quiz 1 Question 1.e.E , the following statement is true:

A ping-pong ball moving near the speed of light still looks
spherical.TRUE /
FALSE (circle one).
http://ocw.mit.edu/NR/rdonlyres/17B4BD2F-8932-49D2-9C7B-D1D2315965C9/0/quiz1_2006_sol.pdf

when in fact it is measured to be an ellipsoid, according to Einstein:
"A rigid body which, measured in a state of rest, has the form of a
sphere,
therefore has in a state of motion--viewed from the stationary
system--the
form of an ellipsoid"
http://www.fourmilab.ch/etexts/einstein/specrel/www/

What am I missing?

The difference between 'looks' and 'measured'.

'Looks' refers to what you would actually see if you were to look at an
object (or photograph it). Light from different parts of the object takes
different lengths of time to reach you, thus the distance the object moves
whilst the light is in motion varies from part to part of the object.
This
causes the viewed shape of the object to be distorted.

See:
http://en.wikipedia.org/wiki/Terrell_rotation

'Measured' us usually taken to be what is determined to be the case
after the finite transit time of light (or other observation method) has
been taken into account.

A relatively moving sphere is (measured to be) deformed into an
ellipsoid but the deformation of the image due to the transit time
of light deforms this back into a sphere.

Look out for the crackpots!

Aha .. indeed .. I missed his 'looks' (and the link didn't work for me)


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