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Haliday-Resnick-Walker state that the escape velocity will cause a projectile to move upward forever, theoretically coming to rest only at infinity.

I was wondering what the forces forcing the body to come to rest at infinity are when the authors are using the word"theoretically".Your help is appreciated.

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"at infinity" is not a physical place, that is more a question of mathematical philosophy. I'd prefer formulations with "approaching infinity" etc. The word theroretical is often misused, even by physicists :=( –  Georg Nov 12 '11 at 11:51

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up vote 3 down vote accepted

It's gravity. Gravity is the force that attracts the projectile to the thing it's escaping from, so gravity is the force that brings it closer and closer to rest as it gets further away.

You could also talk about the escape velocity of a charged particle from another (oppositely) charged particle, and in that case the electromagnetic force would be the dominant contribution. But for whatever reason, people don't usually talk about escape velocity in reference to electromagnetism.

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Thank you.I knew it was obviously one of the factors,but got a bit confused with the way they stated it. –  Eisen Nov 12 '11 at 7:35

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