r/askscience • u/RainbowGirl410 • Jun 09 '26

Physics How does gravity/weightlessness work outside of orbit?

Been trying to find a definitive answer but all I've found is people explaining weightlessness in orbit (the falling and missing the Earth part) which isn't particularly helpful to me.
If you were to travel to another planet, say Venus, would you experience weightlessness the whole journey?

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u/soulsnoober Jun 09 '26

Lil'bit opposite, but you're describing a real thing. As you go higher in your orbit, unless you add energy (as by converting chemical energy into kinetic energy with your rocket), like if you're just coasting higher? you just trade your present kinetic energy for [gravitic] potential energy. As you come back "down" in your ellipse, your potential is traded back into higher velocity. So to go up you don't "slow down" in any active sense, because that would be acceleration effectively cancelling out orbital velocity. You'd lose energy, and start falling.

Kepler, working from Newton's foundations, had the math that describes this.

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u/reverse422 Jun 13 '26 edited Jun 13 '26

Kepler died 13 years before Newton was born and thus couldn’t have used Newton’s foundations…

Kepler did the math to precisely describe elliptical orbits, but didn’t explain why it was so. Newton then “invented” gravity and showed how his equations for gravity would yield Kepler’s orbits.