Equations of motion unsolvable with elementary method

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Discussion Overview

The discussion revolves around identifying equations of motion that cannot be solved using elementary methods, particularly those accessible with high school mathematics. Participants explore examples and methods for simulating these equations to approximate outcomes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • Robin seeks equations of motion that are unsolvable with elementary methods, mentioning a specific case involving a body attached to an ideal spring that can rotate freely.
  • One participant suggests that real-world problems are often too complex for closed-form solutions and are typically simulated in small time steps, calculating forces and moments at each step.
  • Robin reflects on the desire to discover personal equations rather than just collecting examples, sharing an experience from a physics competition where the problem was presented without a clear method for solving it.
  • Another participant proposes the equation of motion for a simple pendulum, noting that while it is solvable with small angle approximations, larger angles require elliptic functions for a solution.
  • This example of the pendulum is reiterated by another participant, emphasizing its utility in simulations to demonstrate deviations from sinusoidal motion at larger angles.
  • Robin expresses gratitude for the pendulum example and indicates an intention to try it in their simulation.
  • Robin also mentions experiencing difficulties with their first simulation, linking to another thread for assistance.

Areas of Agreement / Disagreement

Participants generally agree on the complexity of real-world problems and the utility of simulations, but there is no consensus on a definitive list of unsolvable equations or methods beyond the examples provided.

Contextual Notes

The discussion does not resolve the limitations of the examples provided, nor does it clarify the specific conditions under which the equations are deemed unsolvable.

Who May Find This Useful

Individuals interested in physics simulations, particularly those exploring complex equations of motion and their numerical solutions.

Robin04
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Hi,

Can you help me in collecting equations of motion that are unsolvable with elementary methods (especially with high school maths)? One that I found is when I release a body attached to an ideal spring that can freely rotate around an axis. The reason why I need them is because I would like to make simulations that can calculate a close outcome of the equation of motion.

Thanks for your answer in advance!

Robin
 
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Are you looking for simple equations to check your simulation or are you looking for equations to use in your simulation? Real-world problems are usually too complicated to calculate a closed form solution. They are simulated in small time steps (say, 1/50 second). The forces and moments are calculated for the positions at one time. Then the motion is calculated for the small time step and new positions are obtained. Step through the simulation one time step (aka "time frame") at a time.
 
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After thinking it over again maybe that's not equations that I'm looking for. It would be much more fun to find my own equations. This example I wrote about was an exercise at a physics competition where only the situation/problem was described, and there was no information on how to solve this problem, they didn't even tell anything about the solvability. The method you described is the one that I used in my program. I determined what forces are acting on the body that are dependent on the position, expressed the acceleration, calculated the velocites and updated the positions.
 
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A good example is the equation of motion for a simple pendulum. It is easily solvable if you make the small angle approximation, but for larger angles the solution requires elliptic functions. You could simulate a pendulum with a large angular displacement and show how the actual motion deviates from the sinusoidal motion predicted in the small angle limit.
 
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phyzguy said:
A good example is the equation of motion for a simple pendulum. It is easily solvable if you make the small angle approximation, but for larger angles the solution requires elliptic functions. You could simulate a pendulum with a large angular displacement and show how the actual motion deviates from the sinusoidal motion predicted in the small angle limit.

Thank you ver much. I'll try this one. :)
 

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