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Name: Ayed  R. R.
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: 1/13/2003
Question:
if we have a spacecraft that has a stationary electron inside it, and this spacecraft moving with an acceleration, according to an observer inside it the electron is not moving so it will not radiate electromagnetic wave, but according to an observer outside this spacecraft will see the electron moving with acceleration so it will radiate an electromagnetic wave.What will happen? Will it radiate or will not?

Replies:
Notice that the spacecraft is accelerating, so to keep the electron stationary in the spacecraft, it is necessary to exert a force on the electron so it will accelerate at the same rate as the spacecraft. Therefore, it will radiate due to being accelerated, whether seen by a stationary observer external to the spacecraft or seen by an observer in the spacecraft being accelerated with the spacecraft (and the electron).

You ask a good question about a matter which has confused many people. Just remember that for the electron not to be moving relative to the spacecraft it must be accelerated at the same rate as the spacecraft.

Best, Dick Plano, Professor of Physics emeritus, Rutgers U.

Ayed,

Relativity as commonly stated does not apply to accelerating frames of reference. An "inertial reference frame" must have zero acceleration. This is because an object can detect its own acceleration. When in a car driving at constant speed and not turning, you can not tell very well whether you are moving. If blindfolded, the only motion you detect for sure is the jittering due to little bumps in the road. These jitters are accelerations. At constant speed you cannot tell whether you are moving forward or backward. On a smooth road, there is essentially no difference between moving and idling the engine. If the driver slams the brake, hits the accelerator, or makes a sharp turn, you know it. The electron will radiate due to the acceleration for everyone. Everyone senses the acceleration.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College


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