Register to reply 
Pendulum Potential energy equation 
Share this thread: 
#1
Feb513, 02:56 AM

P: 4

hello every one
i have this pendulum: i need to stabilize the pendulum in the inverted position , i need to know the potential energy for the pendulum , i read several articles in each one i have a different equation : [itex]V=mgl_{p}cos\alpha[/itex] [itex]V=mgl_{p}cos\alpha[/itex] [itex]V=mgl_{p}(1cos\alpha)[/itex] [itex]V=mgl_{p}(cos\alpha1)[/itex] Now i'am really confused which equation is the correct one? Please help me 


#2
Feb513, 06:18 AM

Mentor
P: 41,476

What are you taking as your reference level? (Where PE = 0.) The pivot? The gravitational PE is given by mgΔy, where Δy is measured from your chosen reference level. Using that you should be able to pick the correct formula.



#3
Feb513, 06:54 AM

P: 4

[itex]P.E=0[/itex] at the vertical position ([itex]\alpha=0[/itex] from the vertical line in the picture above), now which formula should i use :
[itex]P.E=mgl_{p}(1cos\alpha)[/itex] or [itex]P.E=mgl_{p}(cos\alpha1)[/itex] 


#4
Feb513, 07:21 AM

Mentor
P: 41,476

Pendulum Potential energy equation



#5
Feb513, 08:55 AM

P: 4

so:
[itex]\Delta y=[/itex](center of mass levelreference level) not the other way around , am i correct? 


#6
Feb513, 10:46 AM

Mentor
P: 41,476

Since you are choosing the reference level to be where the pendulum is vertical (the angle is zero) and thus the mass is at its highest point, all values for y and thus PE for nonzero angles will be negative since they are below that point. 


#7
Feb513, 11:33 AM

P: 4

Now i understand , thank you very much for you kindly help,I'm very appreciative



Register to reply 
Related Discussions  
Pendulum Problem: Potential energy equals? kinetic energy  Introductory Physics Homework  2  
Pendulum (Conservative Forces and Potential Energy  Introductory Physics Homework  4  
Ballistic Pendulum  Kinetic Energy vs Gravitational Potential Energy  General Physics  13  
Potential energy and a pendulum  Introductory Physics Homework  10  
Potential energy of a pendulum when the angle is small  Introductory Physics Homework  13 