
#1
Nov2912, 05:49 PM

P: 123

Why is change in potential energy is defined as
PE1  PE0 = W I mean I could see it for example for gravity if we took PE0 to be zero at ground and we integerated mgy(y^) we get mg(y0  y1) > mgh,but is their a proof somewhere where it shows it will be always negative work ? Thank you. 



#2
Nov2912, 11:14 PM

Homework
Sci Advisor
HW Helper
Thanks ∞
P: 9,205

It won't always be negative work. If the potential energy increases, PE1 > PE0, so W < 0. That says that rather than doing work the system absorbed work. If the potential energy reduces, PE1 < PE0, so W > 0.




#3
Nov3012, 01:47 AM

PF Gold
P: 4,207

W, is work, defined as energy lost from the system. If energy is gained, the system has lost negative work. It's just a convention of direction of energy flow between environment and system.




#4
Nov3012, 06:28 PM

P: 123

Definition of potential energy
Thank you guys that makes perfect sense.




#5
Nov3012, 09:11 PM

Mentor
P: 11,251

The force that you exert on the object as you lift it is equal in magnitude and opposite in direction to the gravitational force on the object. Therefore the gravitational force does work on the object that is equal in magnitude but with opposite sign to the work that you do. Therefore we can also write PE_{final}  PE_{initial} = W_{gravity} 


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