U = -(GMm/r); In outerspace why do we say U "decreases" to zero? Doesn't it increase to zero?

[Gauss44]

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Title says it all.

(I read some previous threads indirectly or somewhat related to this. However, no quality answer yet that I've found.)

EDIT: This is about a spaceship's potential energy becoming zero as a result of traveling far enough away from earth. (Zero potential energy due to being far from the earth's surface, NOT on the earth's surface.)

 

[Teleologist]

Potential energy is generally negative so 0 is the highest value. PE does increase. To 0.

 

[Chrisz]

Because we only care about the different in potential energy when a particle or mass moves from from one state to another. Defining the farthest point from earth to be zero is an arbitrary practice. Below is how the potential energy formula is derived.

du=-dw=-Fdr

Uf-Ui=integral (from r=Ri to r=infinity)[-Fdr]
F=GMm/r^2 Lets define Uf=0 when Rf=infinity
0-Ui=integral (from r=Ri to r=infinity)[-GMm/r^2dr]
Ui=integral (from r=Ri to r=infinity)[GMm/r^2dr]
Ui=-GMm/Ri

See when we derive this formula, we arbitrarily define Uf=0 when Rf=infinity

 

[Gauss44]

Thank you very much.