Double pendulum velocity derivation

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SUMMARY

The discussion focuses on the derivation of the velocity of the second mass in a double pendulum system using Lagrangian mechanics. The first mass's velocity is derived as v_1^2 = l_1^2\dot\theta_1^2, while the second mass's velocity is expressed as v_2^2 = l_1^2\dot\theta_1^2 + l_2^2\dot\theta_2^2 + 2l_1l_2\dot\theta_1\dot\theta_2\cos{(\theta_1-\theta_2)}. The derivation process involves understanding the relationship between the angles of the two rods and their respective angular velocities. The user successfully resolved their query by referencing a reliable source on double pendulums.

PREREQUISITES
  • Understanding of Lagrangian mechanics
  • Familiarity with angular velocity notation (e.g., \dot\theta)
  • Knowledge of trigonometric identities, particularly cosine
  • Basic concepts of pendulum dynamics
NEXT STEPS
  • Study the derivation of kinetic energy in Lagrangian mechanics
  • Explore the dynamics of multi-body systems in physics
  • Learn about the stability analysis of double pendulums
  • Investigate numerical simulations of chaotic systems, such as double pendulums
USEFUL FOR

Students and enthusiasts of classical mechanics, particularly those interested in advanced topics like Lagrangian dynamics and chaotic systems. This discussion is beneficial for anyone studying the behavior of double pendulums and their velocity derivations.

TheFerruccio
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I'm doing a personal project and I'm refreshing my knowledge on Lagrangian mechanics. Right now, I am looking at the double pendulum example. How is the velocity of the 2nd mass derived, in terms of the angles of the two rods? 2nd mass as in, the mass that hangs lowest.

I have not been able to figure out the procedure to doing a derivation. The first mass velocity is relatively straightforward.
 
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I should probably give examples:

I got [tex]v_1^2[/tex] rather easily:

[tex]v_1^2 = l_1^2\dot\theta_1^2[/tex]

But, v2 is expressed as:

[tex]v_2^2 = l_1^2\dot\theta_1^2+l_2^2\dot\theta_2^2+2l_1l_2\dot\theta_1\dot\theta_2\cos{(\theta_1-\theta_2)}[/tex]

I am getting the information from this page:

http://scienceworld.wolfram.com/physics/DoublePendulum.html
 
Last edited:
I figured it out! Never mind!
 

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