Physical pendulum with air friction

AI Thread Summary
The discussion revolves around deriving the differential equation and period of a physical pendulum with air friction. The user acknowledges the need to apply Stokes' equation for air friction but struggles to incorporate it into their calculations. They express a preference for modeling friction as a force proportional to velocity, represented as -k.v, and seek guidance on how to integrate this force into the differential equation. The conversation highlights the complexity of including air friction in the pendulum's motion and the importance of understanding the underlying physics. Ultimately, the user aims to derive the equation while considering the effects of air resistance.
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Homework Statement



For my control system course i need to derive differential equation and period of a physical pendulum.
Pendulum rod's mass is m, length is l and has a spherical mass M

Homework Equations



i need relevant equatins so obviously :D

The Attempt at a Solution



i know that i should use stoke's equation for air firicition but i couldn't find out how.
in some posts period of a physical pendulum is given but i need to solve max. angle

Thank andd sorry about my crappy englisf.İ hope i can define my question
 
Physics news on Phys.org
http://hyperphysics.phy-astr.gsu.edu/hbase/pendp.html#c1

Learn this first, then worry about the air friction, if you're in a course that's apparently wanting you to use an advanced differential equation and you're asking for pendulum equations, you probably need to do some reading
 
i know the pyhsical pendulum. İ do not need to solve differantial equation.İ just need to derive it.İ find a lot of sources about it but none of them include air friction.
and thaks for the reply
 
You probably don't have to go back to "Navier-Stokes". Generally speaking, friction can be modeled by -k dy/dx or -k(d^2y/dx^2). Which do you think is approriate here?
 
i think -k.v is more approriate for my case
 
If it's a control systems course I wouldn't put it past an engineering demon professor to have required it with navier stokes. But yah, if they just said model air friction, throwing in a velocity or velocity squared dependent force makes it plenty difficult I'd think
 
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This is the differential equation of a physical pendulum with no air friction.
In my case there will be a force because of friction and it will be -k.v

My problem is how to include this force to the dif. equ. and what will be the k?
 

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