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# Length contraction

الكلية كلية التربية للعلوم الصرفة     القسم قسم الفيزياء     المرحلة 3
أستاذ المادة فؤاد عطية مجيد       04/11/2018 19:09:30
Now suppose the observer O wants to measure the length of the
spaceship. He can only do this by making an instantaneous measurement of
the spatial coordinates of the end of the ship i.e. A x and B x .
Figure 7.8: Length contraction
The Lorentz transformations give:

To continue our discussion of the Lorentz transformations and relativistic
effects, we consider the famous ``twin paradox of Peter and Paul. When they
are old enough to drive a spaceship, Paul flies away from earth at very high
speed. Because Peter, who is left on the ground, sees Paul going so fast, all of
Pauls clocks appear to go slower, from Peter s point of view. Of course, Paul
notices nothing unusual. After a while he returns and finds that he is younger
that Peter! Now some people might say ``heh, heh, heh, from the point of view
of Paul, can t we say that Peter was moving and should therefore appear to
age more slowly? By symmetry, the only possible result is that they are both
the same age when they meet . But in order for them to come back together
and make a comparison, Paul must turn around which involves decelerating
and accelerating and during that period he is not in an inertial frame. This
breaks the apparent symmetry and so resolves the paradox.

Example: 1
(a) An observer on Earth sees a spaceship at an altitude of 4350 km moving
downward toward Earth with a speed of 0.970c. What is the distance
from the spaceship to Earth as measured by the spaceship’s captain?
(b) After firing his engines, the captain measures her ship’s altitude as 267
km, while the observer on Earth measures it to be 625 km. What is the
speed of the spaceship at this instant?

المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .