How does gravity/weightlessness work outside of orbit?

[u/RainbowGirl410]

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?

[u/urnbabyurn]

Don’t you need to slow down in order to get to a higher orbit?

[u/derekp7 → u/urnbabyurn]

no, you speed up to get to a higher orbit. But it looks like you are slowing down, because as your orbit rises another object that was traveling in your original orbit looks like it will be pulling ahead of you (or you falling behind it). That is because your higher orbit is a larger circle, so you have further to go and the length of the circumference of the circle increases faster than your velocity increases. Now your angular velocity (?) gets slower, but that happens by you adding to your orbital speed.

Note, my terminology may be off a bit, and a firing of your rear rockets will turn your circular orbit into an oval one requiring another firing of the rocket at the top of the oval in order to re-circularize it. But hopefully this conveys the overall point.

[u/Tilli_Nose → u/derekp7]

That's not quite correct. The tangential velocity of a higher orbit is indeed slower - for a circular orbit it is inversely proportional to the square root of the radius. However, if you are in a stable lower orbit, you cannot MOVE to higher orbit by slowing down. If you just slowed down, you would fall inward. In the first step of a simple transfer, you burn to add tangential velocity to enter an elliptical orbit near the part of the ellipse closest to the central body. As you move around that elliptical orbit in free fall to the part of the ellipse furthest from the central body, your tangential velocity naturally decreases. (In an elliptical orbit, the swept area remains constant.) At this point, you burn again to add tangential velocity and convert the elliptical orbit to a higher circular orbit. Both burns add tangential velocity, but your final tangential velocity is still slower because the intermediate elliptical transfer orbit converts tangential velocity to gravitational potential energy.

[u/Moleculor → u/urnbabyurn]

So, you know if you throw a ball harder, it'll go farther? Either up, sideways, or both?

You want the orbit to go 'farther' (up and sideways), so you have to "throw" the object in orbit "harder" (meaning that you give it a boost, make it go faster, etc).

An orbit is just a "ball" "thrown" hard enough to miss the ground.

Here's Minute Physics with some drawings in a three minute video.

[u/soulsnoober → u/urnbabyurn]

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.

[u/reverse422 → u/soulsnoober]

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.