Long Bar and the Speed of Light

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SUMMARY

The discussion centers on the propagation of mechanical waves in a long bar when a force is applied. It is established that the other end of the bar will not respond instantaneously; instead, a mechanical wave will propagate at the speed of sound within the material. If the force exceeds the speed of sound, the bar will break, generating a wave that also travels at the speed of sound. This aligns with the principles of special relativity, confirming that no information can travel faster than the speed of light.

PREREQUISITES
  • Understanding of mechanical waves and sound propagation
  • Basic knowledge of special relativity principles
  • Familiarity with longitudinal waves and their characteristics
  • Concept of material properties affecting wave speed
NEXT STEPS
  • Research the speed of sound in various materials
  • Learn about mechanical wave propagation and its applications
  • Explore the implications of special relativity on information transfer
  • Investigate the effects of exceeding material strength limits
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Physics students, engineers, and anyone interested in the mechanics of wave propagation and the implications of special relativity in material science.

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I was asked this today, and I cannot picture an answer. Say you had a long bar in a vacuum, billions of miles long. If a force was applied lengthwise on one end, would the other end immediately respond? Would reference frames matter in this instance? I know information cannot travel faster than the speed of light, and I have a basic understanding of special relatively, but i cannot picture what would happen in this case...
 
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There are lots of threads about this. Perhaps someone who participated in one of them can post a link.

The other end will not respond immediately. You will just create a mechanical wave that propagates at the speed of sound. (A longitudinal mechanical wave is, by definition, sound). If you hit it with a hammer that's moving faster than the speed of sound in that material, then you'll just break it and create a wave the propagates at the speed of sound.
 

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