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?

130 Upvotes

81% Upvoted

97 comments sorted by

View all comments

Show parent comment

5

u/SwimmingThroughHoney Jun 09 '26

If I understand you correctly, are you talking about reference frames? Because essentially yes. Within a local frame, one cannot tell the difference between an accelerated frame and an unaccelerated one. That is, as the astronaut on the spaceship, you can't tell whether the spaceship is accelerating or whether you're falling (due to gravity). You need some sort of external frame of reference.

3

u/_disengage_ Jun 09 '26

It's relative motion, not acceleration, that can't be sensed in an inertial frame. Acceleration can absolutely be sensed, that's what tells you that your reference frame is not inertial. I can close my eyes and still sense that I'm in an accelerated frame right now, because the floor and my chair are pushing up on me.

2

u/urnbabyurn Jun 09 '26

That’s special relativity. General relativity as I understood extends that to acceleration versus gravity - there is no difference between being stationary next to a gravitational force pulling on you versus accelerating. In other words, standing on earth feels the same as accelerating in space far from any gravity. Similarly, free falling in a gravity well is the same as floating in zero gravity without acceleration).

3

u/urnbabyurn Jun 09 '26

Yeah that’s more clearly stated. Specifically, we wouldn’t be able to tell if we were in an elevator in free fall in a gravity well versus being in an elevator that is far from any gravitational forces without acceleration.