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horsetuna t1_j2z4uva wrote

Reply to comment by Weed_O_Whirler in How fast would a body fall to earth if there was no atmosphere to stop it from accelerating past a terminal velocity? by straubzilla

If I may ask, the rule/law that your energy must be zero is the Law of Conservation of Energy right?

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Redbelly98 t1_j2zg3bh wrote

Not quite. There is no law that says the energy must be zero. That was just a starting assumption in order to arrive at some kind of answer.

What Conservation of Energy says is that the total energy (potential + kinetic) does not change as the body moves toward Earth. If it starts at zero energy, then the energy remains zero. But the energy could have started with some other value too.

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Master-of-Ceremony t1_j31pqtm wrote

More accurately, it’s just that you’ve defined you’re potential to be zero at infinity. You could’ve defined it to be anything (finite) at infinity so long as you remember to add that to the energy you have at radius r too

There’s important distinction between assuming and defining!

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