Example & Question: What Will Clock 3 Count?

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Discussion Overview

The discussion revolves around a thought experiment involving clocks and light, specifically focusing on what Clock 3 will register when a light signal reaches it. The context includes diagrams illustrating the scenario and the relative motion of a plane and the clocks.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants assert that the diagrams are correct and that the plane moves at half the speed of light, affecting how the clocks register time.
  • One participant calculates that it will take 1.5 seconds for light to reach Clock 3 in one scenario and 1 second in another, questioning what Clock 3 will actually count.
  • Another participant clarifies that the third diagram is misleading, suggesting that it should indicate the clock on the plane shows 1 second instead of implying that all clocks show 1 second.
  • There is a suggestion that the speed of the light bulb and the clocks should be referred to as c/2 rather than the plane's speed.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the diagrams and the timing of the light reaching Clock 3, indicating that the discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are potential ambiguities in the diagrams and the definitions of speed and time as they relate to the clocks and the light signal, which may affect participants' understanding of the scenario.

Who May Find This Useful

Individuals interested in the concepts of relativity, time dilation, and the behavior of light in moving reference frames may find this discussion relevant.

ghost11
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Hi guys
is the example true?
what will the clock 3 count when the light reach it

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Welcome to PF! Move towards the light!

Hi ghost11! Welcome to PF! :smile:

Yes, the diagrams are correct …

the lamp and the clocks are stationary, and the plane is going half as fast as the light, so in the clocks' frame (middle diagram), the plane will reach the first clock at the same time as the light reaches the second clock.

And in the plane's frame (bottom diagram), a ray of light is moving left, and the clocks are moving right, half as fast as the light …

(and of course they're closer together, but that won't make any difference)

so when the first clock reaches the plane, the third clock will have moved towards the light.
ghost11 said:
what will the clock 3 count when the light reach it

You do the maths (no square-roots needed! :wink:) …

what equations do you get?

Hint: move towards the light, ghost11! :smile:​
 
thank you tiny-tim
in the second and third diagram the clocks count 1 second!
in the second diagram it will take 1.5 second for the light to reach clock 3
in the third diagram it will take 1 second for the light to reach clock 3
what the clock will count for real??
please explane more ... cause iam little slow .. o:)
 
Clock 3 will show 1.5s when the light reaches it. The third diagram is a bit confusing. It shouldn't say "clocks 1s". It should say that the clock on the plane shows 1s. Also, it shouldn't say that the plane's speed is c/2. It should say that the speed of the light bulb and the clocks in the picture is c/2.
 
Fredrik thank you a lot
I didn't see it that way ... i understand now
 

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