The Length of Pendulum Strings: Motion Effects

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Discussion Overview

The discussion revolves around the effects of motion on the perceived length of a pendulum string, particularly in the context of special relativity. Participants explore how the motion of the pendulum affects measurements of its length and time period from different reference frames.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions whether the length of the pendulum string appears contracted when the pendulum is in motion, noting that the string's orientation changes relative to the direction of motion.
  • Another participant asks for clarification on whose point of view is being considered regarding the perceived contraction of the string.
  • A participant suggests that from an inertial observer's perspective, the length of the string remains unchanged according to special relativity, despite the pendulum's motion.
  • Some participants speculate that the original poster (OP) may be considering a pendulum in a moving rocket, while others propose different experimental setups involving charged particles.
  • The OP clarifies that they are referring to a pendulum moving at a constant velocity relative to a frame and questions how this affects the length of the string and the time period as viewed from another rest frame.
  • The OP presents a formula for the time period of the pendulum as viewed from different frames, suggesting a relationship involving the Lorentz factor.

Areas of Agreement / Disagreement

Participants express differing views on whether the length of the pendulum string appears contracted and how to interpret the effects of motion on the time period. The discussion remains unresolved, with multiple competing perspectives presented.

Contextual Notes

There are limitations in the assumptions made about the reference frames and the conditions under which the pendulum is observed. The discussion does not resolve the mathematical implications of the proposed time period formula.

anantchowdhary
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When a pendulum is moving

will the length of the string that the bob is attached to appear to be contracted?I have this doubt as the string is sometimes in direction of motion and at one point absolutely not in the direction of motion
 
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Appear to be contracted from whom's point of view?
 
From an observer's point of view whoo is in an inertial frame.If he wants to calculate the time period of the pendulum,how will he measure the length as it changes from position to position
 
Please answer!:D
 
Please sum1 help me out here!
 
anantchowdhary said:
When a pendulum is moving

will the length of the string that the bob is attached to appear to be contracted?I have this doubt as the string is sometimes in direction of motion and at one point absolutely not in the direction of motion
Each infinittesimal portion of the string is a linie segment which is moving perpendicular to its motion. According to SR the length of the string will remain unchanged.

Pete
 
I assume that the OP meant that the swinging pendulum was in a moving rocket (say) being observed from the earth.
 
Doc Al said:
I assume that the OP meant that the swinging pendulum was in a moving rocket (say) being observed from the earth.
That's the usual way. Another way is to to have a charged particle on a string at a fixed distance from a charged plate. But you're right, he was probaby speaking of in a grav-field or in a rocket shift.

Pete
 
Doc Al said:
I assume that the OP meant that the swinging pendulum was in a moving rocket (say) being observed from the earth.

No,i just meant to have an experiment of a pendulum,moving at a constant velocity relative to a frame.Now the string of the pendulum,once is perpendicular to the direction of motion,and when it is at its maxima,it has some component in the direction of velocity,so my question was,wouldnt this affect the length of the string?

Also the time period as viewed from another rest frame would be the
[tex]T = \gamma T_0[/tex]?

where T is the time period as viewed by the rest frame and [tex]T_0[/tex] ,[tex]T[/tex]the time period as viewed by the moving frame.
 
Last edited:
  • #10
PLease help.I would really ,like to know whether the above reasoning is correct or not!
 

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