Pendulum Using Lagrange And Hamilton

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Discussion Overview

The discussion revolves around a problem involving a pendulum with its support point accelerating vertically upward. Participants explore how to determine the period of the pendulum under these conditions, utilizing concepts from Lagrangian and Hamiltonian mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that the period of the pendulum can be approximated as \(2\pi(L/(g-a))^{1/2}\), where \(a\) is the upward acceleration.
  • Another participant recommends using polar coordinates to express the position and velocities, emphasizing the need to account for both gravitational and upward acceleration when calculating kinetic and potential energies.
  • A different viewpoint asserts that the formula for the period \( \nu = 2\pi \sqrt{\frac{L}{g}} \) is merely an approximation and that the exact expression cannot be solved straightforwardly.
  • A later reply prompts the original poster to consider the scenario where the upward acceleration equals \(g\) to further analyze the period.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the correct expression for the period of the pendulum, with multiple competing views and approaches presented throughout the discussion.

Contextual Notes

There are unresolved assumptions regarding the effects of the upward acceleration on the pendulum's dynamics, and the discussion highlights the complexity in deriving an exact solution for the period.

skrao
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i have been given a problem involving a pendulum, where its support point is accelerating vertically upward. The period of the pendulum is required. Anybody have any idea how to start this one? is it not just 2pi(L/g-a)^1/2?
 
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First thing to do is write x, y and x', y' in terms of r and theta (polar coords). Draw a picture to help you visualize, then find the kinetic and potential energies and be sure to take into account the upwards acceleration, so you have both gravity and this upwards accelration acting on the mass. Then find the Lagrangian and/or Hamiltonian and use one of them to find the equations of motion.
 
The period of a pendulum is not [tex]\nu = 2\pi \sqrt{\frac{L}{g}}[/tex] that is only an approximation to the right expression, which we can't solve exactly
 
Last edited:
skrao -- Ask yourself what the period would be if the upward acceleration was equal to g?

Regards,
reilly Atkinson
 

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