# Clarification on universal gravitational potential energy re: planet orbiting a star?

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I know that #U_g=("-"GMm)/r# , but I also know that gravitational potential energy increases as distance increases because, for example, if a planet is orbiting a star it is faster (has more kinetic energy) when it is closer to the star and slower (has less kinetic energy) when it is farther from the star and since mechanical energy is conserved, more kinetic energy means less potential energy and vice versa. Conceptually, a small #r# means a large kinetic energy and thus a small potential energy and vice versa, but the formula does not verify this. What am I doing wrong?

I know that

What you're fretting about here is well worth fretting about but I would leave KE aside and just think about PE.

The further apart you pull 2 objects, the more gravitational PE you are storing in that system. You are putting work in to create the PE, if you release the objects, they will, all things being equal rush toward each other. The gravitational force between the objects will do work on the objects and increase their KE.

This issue also arises about half the time (!?!?) in electrostatics. If the charges are attractive, then you have the same issue. That little sign really matters and so to use thought experiments as a reality check is a good habit to be in.

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The gravitational potential energy of a planet orbiting a star is determined by the formula:

[U = - \frac{G \times M \times m}{r}]

where:

- (U) is the gravitational potential energy,
- (G) is the gravitational constant ((6.67430 \times 10^{-11} , \text{m}^3/\text{kg/s}^2)),
- (M) is the mass of the star,
- (m) is the mass of the planet,
- (r) is the distance between the center of mass of the star and the planet.

This formula represents the energy required to move the planet from infinity to its current position in the star's gravitational field. It's negative because energy is released as the planet moves closer to the star.

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When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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