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typos. Excerpt from book: VI THE THEOREM OF THE ADDITION
OF VELOCITIES EMPLOYED IN CLASSI- CAL MECHANICS LET us
suppose our old friend the railway carriage to be
travelling along the rails with a constant velocity v,
and that a man traverses the length of the carriage in
the direction of travel with a velocity w. How quickly,
or, in other words, with what velocity W does the man
advance relative to the embankment during the process?
The only possible answer seems to result from the
following consideration: If the man were to stand still
for a second, he would advance relative to the
embankment through a distance v equal numerically to the
velocity of the carriage. As a consequence of his
walking, however, he traverses an additional distance w
relative to the carriage, and hence also relative to the
embankment, in this second, the distance w being
numerically equal to the velocity with which he is
walking. Thus in total he covers the distance W = v + w
relative to the embankment in the second considered. We
shall see later that this result, which expresses the
theorem of the addition of velocities employed in
classical mechanics, cannot be maintained; in other
words, the law that we have just written down does not
hold in reality. For the time being, however, we shall
assume its correctness. THE APPARENT INCOMPATIBILITY OF
THE LAW OF PROPAGATION OF LIGHT WITH THE PRINCIPLE OF
RELATIVITY THERE is hardly a simpler law in physics than
that according to which light is propagated in empty
space. Every child at school knows, or believes he
knows, that this propagation takes place in straight
lines with a velocity c =300,000 km./sec. At all events
we know with great exactness that this velocity is the
same for all colours, because if this were not the case,
the minimum of emission would not be observe... |
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