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Okay, so the formula for Gravitational Potential Energy (GPE) of satellites is: $$ U=-GmM/d$$ Mass and distance can't be negative, and $G$ is constant that is not negative.
Why is a satellite's GPE negative?
For other objects, like a ball, the GPE is calculated as: U=mgh
Correct me if I am wrong, but this is what I think:
Satellite's GPE is measured relative to earth's center, while a ball's GPE is measured relative to earth's surface.
The satellite was sent to its orbit with energy from the fuel, and it was launched from the earth's surface. While for the ball, it was sent to its height with energy (say, from a human body) and it was carried from the earth's surface.
So is a satellite's GPE negative because: Energy needed to bring the satellite to earth's center is greater than the energy expended when it was sent to orbit?