Why is potential energy considered negative in an inversed pendulum system?

AI Thread Summary
In an inverted pendulum system, potential energy (PE) is defined as PE = mgz, where z is negative since the coordinate system is oriented upwards. The confusion arises from the textbook's treatment of height (h), which appears to take its absolute value, leading to questions about the reference point for zero height. The rest position of the pendulum aligns with the origin (O), which clarifies the negative work done by the pendulum due to its angle. Ultimately, the discussion highlights the importance of defining the coordinate system and reference points in understanding potential energy in this context. The thread concludes with a request to close the discussion due to the initial misunderstanding.
Andrax
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we have an inversed pendulum(ignore the car)
cart.gif

and we choose the coordinate system to be upwards
the potential energy PE=mgz (z will be hegative since( O,k) is upwards right?) z is always under O.
but in the textbook they basically take the absolute value of h i don't understand why?
 
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Where is the textbook putting the zero of h?
 
ModusPwnd said:
Where is the textbook putting the zero of h?

at the point of rest of the pendulum (same as O)
 
fixed the problem (h ad to do with angle being negatgive which means the work of p is negative)
sorry my explication of the question was off , close this thread
 

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