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24-Ruby III

## Pendulum ODE

Prime 5 - a constant not function as an answer!

See the attach and help me please!

5 REPLIES 5
24-Ruby V
(To:ValeryOchkov)

Two problems in your MC15 sheet:

1) wrong syntax of Odesolve (you don't have to provide the function name theta in MC15)

2) the expression on the right hand side of your ODE takes non-real values if theta goes above 45 degree
I coped boldly with the last situation by applying the Re() function 😉

Now you get a solution, but its constant 45°

24-Ruby III
(To:Werner_E)

Thanks!

But why I get a constants, not a function - angle of the pendulum as function of time?

Total energy is constant throughout, so the value under the square root sign of the numerator of the RHS of your ODE is always zero; hence theta goes nowhere (as you can see from Werner's graph)!!

Alan

If you wish to get the equations of motion from conservation of energy Val, you need to do the following:

Alan

24-Ruby III
(To:AlanStevens)

Thanks Alan!

I see my bug!

See please Problem 3 in the Manuscript!

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