Centrifugal Force as Artificial Gravity

Electric Skeptic

Well-known member
It's not flawed.

You can prove it by going to your neighborhood playground, jumping on the great merry-go-round that spins horizontally to the ground. The kind kids speed up by kicking their legs against the ground as it spins:

View attachment 1534

Once it's spinning pretty fast, walk to the center and see what it feels like. Then walk to to the edge and do the same.

"Gravity" increases the further away from the hub you are.
No offense, but that demonstration has nothing to do with the question I actually asked.
 

Electric Skeptic

Well-known member
It's pretty good.

I wont turn this thread into a "favorite sci-fi book" fest, but if we're listing good books that should have been more influential, I'd point to Asimov's Foundation series, as well as Julian May's Saga of Pleistocene Exile. The latter is possibly my all-time fav.
The original 3 Foundation books - yes. But even Asimov hated the series by the time he finished. The later sequels...not so much.

I really enjoyed the Saga...the first few books. Then it got less and less interesting to me.

In my experience there have been a lot of wonderful books which, when extended into a series (whether that was intended all along or decided upon solely based on the success of the first book) fail very badly, with each successive book getting worse and worse. The classic example (to me, at least) is Dune. Fantastic book. Wonderful. Top ten science fiction books of all time, IMO. The rest of the series was an unmitigated disaster.
 

Whateverman

Well-known member
No offense, but that demonstration has nothing to do with the question I actually asked.
No offense taken. You're right, it wasn't the best analogy - but the thing is the force away from the merry-go-round axis will exist even if you're not touching the surface. Try it; jump up high once the merry-go-round is spinning; you'll be thrown towards the edge.

This is because even if you're not touching the surface, you're still moving in circles around the axis - which is the source of the "gravity".

I'm not a physicist, and my grades in physics weren't great :D Still, I believe if you think about it, you'll realize there'll be a force towards the hull even if you're "hovering" - and that's because you're still moving around the axis even when you hover.
 

Nouveau

Well-known member
No offense taken. You're right, it wasn't the best analogy - but the thing is the force away from the merry-go-round axis will exist even if you're not touching the surface. Try it; jump up high once the merry-go-round is spinning; you'll be thrown towards the edge.

This is because even if you're not touching the surface, you're still moving in circles around the axis - which is the source of the "gravity".

I'm not a physicist, and my grades in physics weren't great :D Still, I believe if you think about it, you'll realize there'll be a force towards the hull even if you're "hovering" - and that's because you're still moving around the axis even when you hover.
I think the point is that without some contact or connection with the spinning outer surface, you wouldn't be spinning around the axis. That motion will generate centrifugal force, but to get that motion one has to be somehow connected to the spinning surface. The force isn't generated by some magical field permeating the space between the axis and the spinning surface. It's that anything being made to spin around the axis is continually being accelerated towards the center, while it's inertia makes it want to shoot off in a straight line. So something hovering in a vacuum between the axis and the surface without moving around the axis would not feel any spin gravity. The same concept is also present in The Expanse TV series and novels.
 

Whateverman

Well-known member
I think the point is that without some contact or connection with the spinning outer surface.
How does someone launch the craft, other than from the hull? If you're on the hull, you're rotating around the axis, even if you jump in the air. Even if you jump at the axis point down at the end of the tube, you're still rotating slightly...

Anyhoo, I'm not going to turn this into a debate about physics; I've already admitted my expertise in the field is limited :)
 

Nouveau

Well-known member
How does someone launch the craft, other than from the hull? If you're on the hull, you're rotating around the axis, even if you jump in the air. Even if you jump at the axis point down at the end of the tube, you're still rotating slightly...

Anyhoo, I'm not going to turn this into a debate about physics; I've already admitted my expertise in the field is limited :)
If jumping/launching from the surface, then you've already been accelerated to generate spin gravity. If you jumped inside the spinning cylinder (in a vacuum) and were able to use a rocket pack for long enough to return you to a non-rotating frame with respect to the axis, then you would cease to experience any spin gravity. The spin gravity comes from the spinning motion around the axis, and not merely from being inside something that is spinning around that axis. At least, that's my equally non-expert understanding :)
 

Electric Skeptic

Well-known member
If jumping/launching from the surface, then you've already been accelerated to generate spin gravity. If you jumped inside the spinning cylinder (in a vacuum) and were able to use a rocket pack for long enough to return you to a non-rotating frame with respect to the axis, then you would cease to experience any spin gravity. The spin gravity comes from the spinning motion around the axis, and not merely from being inside something that is spinning around that axis. At least, that's my equally non-expert understanding :)
I think, from the combined wisdom of all who've contributed to this thread (most of them with more knowledge on the subject than I), the following appears to be the case.

Inside a theoretical kilometers-wide rotating cylinder:
- any person standing on the inside of the hull would feel a pseudo-gravity.
- if the interior of the cylinder were a vacuum, and a person were magically placed, say, a foot above the inside of the hull, that person would feel no pseudo-gravity. Going back to my question in the OP, Jimmy (I remembered his name!) on his aircraft (Dragonfly?) would not feel more pseudo-gravity as he moved away from the axis of rotation. He'd continue to feel no pseudo-gravity at all until he made contact with the inside of the hull...at which case he would do so.
- if the interior of the cylinder were not a vacuum, then whatever gas fills it would also be moving in concert with it. So our magical person placed a foot above the inside of the hull would be subject to the centrifugal force not of the spinning object, but of the gas inside it which is rotating in concert with it. Going back to Jimmy, as he moved further away from the axis of rotation, (a) the atmosphere would grow thicker and (b) the atmosphere would be moving more quickly. Those two things would combine to increase his pseudo-weight as he moved further away from the axis until, when he got to ground level, he'd have his maximum pseudo-weight given the strength of the pseudo-gravity.

I think.
 

Rahab

New Member
We're probably all familiar with the idea of a spaceship (with at least some parts) rotating, to produce artificial gravity. There's that memorable sequence in 2001 of Poole running around the loop, for example.

In Rendezvous With Rama, Arthur C. Clarke has a miles long spaceship that is a huge hollow cylinder (imagine a big oil drum, but miles long). It rotates to produce artificial gravity on the inside of its hull.

Part of the consequent physics he describes is that at the axis of rotation, there is zero gravity (I'll stop using 'artificial' all the time; take it as read) and as one 'descends' toward the hull of the ship, the gravity increases. At one stage he has a character pedalling a user-propelled aircraft (that is designed, if memory serves, to function in Martian gravity, which is about 1/3 of earths). The character can't fly right at the axis, as there is no gravity at all - his craft won't work, it can't even work out which way is 'up'. So he has to 'descend' a bit until he encounters gravity approximately the same as that for which his craft is intended.

Am I wrong, or is this entire premise flawed? If you imagine a spinning cylinder in a no-gravity field, there would, just like in Clarke's construct, be gravity if you were on the inside of the hull. But would there be a force pulling you down if you were not in contact with the hull? The centrifugal force would only affect that which is in contact with the hull...wouldn't it?

Would it make a difference if the cylinder were filled with air (or some gas) as opposed to being a vacuum?
: First-one-must-define-vacuum.
 
Top