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File 128926287224.jpg - (1.68MB , 2592x1944 , DSC00437.jpg )
1019 No. 1019 [Edit]
Gravitational Potential Energy: described by the equation

Ep = -G*m1*m1/r Where G is the universal gravitation constant, m1 is mass of planet 1, m2 mass of planet 2, and r the distance between the center of mass between planets. For various reasons, they put a negative sign in front of this equation. But you can't have negative energy! Can you figure out why theres a negative sign?
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>> No. 1020 [Edit]
Not a clue.
>> No. 1021 [Edit]
File 128926292831.png - (98.73KB , 500x500 , 1271386795309.png )
>> No. 1022 [Edit]
File 128926294614.jpg - (19.55KB , 510x423 , carl_sagan.jpg )
If I told you I'd have to kill you.
>> No. 1023 [Edit]
Would this possibly be a black hole?
>> No. 1024 [Edit]
if the force is being constructed as a vector the negative sign simply indicates its direction.
the direction being down toward the earth.
>> No. 1025 [Edit]
But this isn't force, but potential energy.

As distance between the two planets increases, the potential energy should increase. But the equation dictates that the potential energy will simply approach zero from the negative side. Whys that?
>> No. 1026 [Edit]
Because it is supposed to be negative.

>This potential energy is more strongly negative than the total potential energy of the system of bodies as such since it also includes the negative gravitational binding energy of each body. The potential energy of the system of bodies as such is the negative of the energy needed to separate the bodies from each other to infinity, while the gravitational binding energy is the energy needed to separate all particles from each other to infinity.
>> No. 2709 [Edit]
It's a good question, the answer is that potential is always relative to a point of reference, and here we choose r = infinity to be the point at zero potential. Then since potential is just the negative integral of work done in bringing that point from infinity to zero, and the work done is positive (because we're going with the gravitation field, not against it), the potential energy is negative.

As for why we don't choose r = 0 to be the point of zero potential, I think it's because the law of gravitation isn't entirely accurate for small distances (since the force blows up to infinity there), and moreover for r=0 they'd need to occupy the same point in space anyway.

That is an increase. It goes from more negative to less negative. Hence the delta is a positive increase.

Post edited on 13th May 2022, 9:04pm
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