The Second postulate is much more difficult to accept, because it violates ourcommon sense which is firmly grounded in the Galilean kinematics that we have learned from everyday experiences It implies that it is impossible to accelerate a particle to a speed greater than c
The Second postulate is much more difficult to accept, because it violates our “ common sense”, which is firmly grounded in the Galilean kinematics that we have learned from everyday experiences. It implies that “it is impossible to accelerate a particle to a speed greater than c
20-3 Consequences of Einstein' s postulates 1.The relativity of time We consider two observers: S is at rest on the ground, and S is in a train moving on a long straight track at constant speed u relative to s The observers carry identical timing devices, illustrated in Fig 20-4, consisting of a flashing light bulb F attached to a detector d and separated by a distance Lo from a mirror m The bulb emits a flash of light that travels to the mirror when the reflected light returns to d, the clock ticks and another flash is triggered
20-3 Consequences of Einstein’s postulates 1.The relativity of time We consider two observers: S is at rest on the ground, and S’ is in a train moving on a long straight track at constant speed u relative to S. The observers carry identical timing devices, illustrated in Fig 20-4, consisting of a flashing light bulb F attached to a detector D and separated by a distance from a mirror M. The bulb emits a flash of light that travels to the mirror, when the reflected light returns to D, the clock ticks and another flash is triggered. L0
The time interval At between ticks is 2L (20-1) The interval At is observed by either s or s when the FD clock is at rest respect to that observer Fig 20-4
The time interval between ticks is: (20-1) The interval is observed by either S or S’ when the clock is at rest respect to that observer. M F D Fig 20-4 L0 0 t c L t 0 0 2 = 0 t
We now consider the situation when one observer looks at a clock carried by the other. Fig 20-5 shows that s observes on the clock carried by s on the moving train B L Fig 20-5 FIDI S FID uAt s
We now consider the situation when one observer looks at a clock carried by the other. Fig 20-5 shows that S observes on the clock carried by S’ on the moving train. F D S A B C L L ' S ' S ' S ut Fig 20-5 F D F D
According to s, the flash is emitted at A, reflected at b. and detected at c This interva△tis 1s2l2/n2 +(l 2 △ (2020) Substituting for Lo from Eg(20-1)and solving Eq(20-2)for At gives △ △t (/)2 (203)
According to S, the flash is emitted at A, reflected at B, and detected at C. This interval is (20-20) Substituting for from Eq(20-1) and solving Eq(20-2) for gives (20-3) c t L u c L t 2 2 0 ) 2 2 ( 2 + = = 2 0 1 ( ) c u t t − = t t L0