/sci/ - Science & Math

Yes, you'd feel a force pulling you down if you jumped. You'd also feel a force at a right angle to you if you fell.

ROTATING REFERENCES FRAMES, TIMOTHY

DIDN'T YOU DO YOUR COORDINATE SUBSTITUTION?

Jump hard enough and you will get stuck in the middle.

>>4532760
If you jumped hard and applied some powerful thrusters you could stay still whilst the cylinder rotated underneath you.

Just like flying a plane really.

>>4532750
this

tangential velocity, bitches... you're ignoring it

>Thus, if you were to, say, jump up, there would be nothing to pull you back down
You haven't spent much time swinging things around in a circle, I take it. Kids need to play more with real objects.

You would still be rotating with the cylinder when you jumped, so you would still feel a force pulling you back to the 'ground'.

>>4532766
Yeah, noting that you'd have to cancel your angular momentum about the cylinder's axis with those thrusters.

you would fall back to the ground, but also some coriolis force wobble you.

>>4532697
I'm Captain Shepard, and this is my favourite store on the citadel.

And the cylinder only simulates gravity while you are rotating with it. That is to say if you were to jump and somehow stop rotating with it, you would seem to float. If you simply jumped then you would land again because your acceleration would be in a straight line, and the movement of the inner surface would not.

>>4532791
Could someone please explain this to me? I roughly understand the concept, but why would an object being stationary affect gravity? Surely you're still within the gravity..

>>4532813

Because it's not 'gravity'

The force pulling you down is the central acceleration due to spinning in a circle; not the mutual attraction of massive bodies.

they just end up having the same magnatide and direction

How would you go into orbit, as it were, in an o'neil cylinder. and wouldn't it be different if you went widdershins

The induced gravity is equal the gravitational field of the earth. If the cylinder is big enough a jumper would fall as if on earth.

>>4532842
CORIOLIS EFFECT YOU DERPS

>>4532840

'orbit' is meaningless because there is no gravity.

also what the fuck is widdershins you pokemon aspie

>>4532851
nothing to do with pokemon

it means against the normal turn, like counter clockwise.

i think you could "orbit" if you were at the same velocity (lets assume stationary) of the cylinders centre of mass. seeing as there are no forces, you'd float.

you might be able to achieve escape velocity by running widdershins

OK I GOT QUESTION YOU CAN ANSWER IN A MILLION YEARS

WHAT IF THE STATION WAS A RING INSIDE A RING, AND THE INNER RING SPAN CLOCKWISE AND THE OUTER RING SPAN ANTI-CLOCKWISE BOTH AT EQUAL SPEED?

>>4532813
Let's say you're on a platform at the end of a string, and it's spinning round so that you get pushed on to the platform. If you jump off of the platform then you stop being pushed in by it, and carry on in a straight line.
Now, if instead of a platform you're standing inside a tube and it's rotating then when you jump up, stop being acted on by the tube, and move in a straight line, you can only hit a side of the tube. Because the tube is rotating, the part you jumped from rotates round to be under you in the time you're moving in a straight line.

I can MS paint it if you want mroe help

Is there any reason we haven't tried making an O'Neil cylinder on land?

>>4532883
It's big, it's expensive, it's potentially dangerous, and it's un-necessary/unable to operate properly. On earth we already have gravity: All simulating would do would be increase the amount that we feel, and put it in an awkward direction.

For things that need a high acceleration we already have centrifuges of various sizes. It'd basically be large, expensive and useless.

>>4532813
Does this help you understand?

The cylinder keeps spinning but you keep the velocity you had while spinning with the cylinder, so its as if you just went up and landed in spot near to wear you left the ground. That said, I'm not willing to say either you or "your associate" are correct.

A small jump would bring you right back to wear you jumped up from, but a very large jump that gives you an "inward" velocity much greater than velocity of the cylinder itself would obviously send you to the other side of the cylinder before the cylinder could catch up. Obviously there is some middle ground between the two. Jumping directly up will cause you to drift forward on the cylinder. The "higher" your jump the further the drift.

>>4532870
Then you've got two basically non-interacting concentric ringworlds with almost the same effective "gravity". Not sure how you'll keep the outer ring lit.

>>4532880
Beautiful, that's fine. I looked at it on wiki, but thanks!

>>4532813
Does this help you understand?

The cylinder keeps spinning but you keep the velocity you had while spinning with the cylinder, so its as if you just went up and landed in spot near to wear you left the ground. That said, I'm not willing to say either you or "your associate" are correct.

A small jump would bring you right back to wear you jumped up from, but a very large jump that gives you an "inward" velocity much greater than velocity of the cylinder itself would obviously send you to the other side of the cylinder before the cylinder could catch up. Obviously there is some middle ground between the two. Jumping directly up will cause you to drift forward on the cylinder. The "higher" your jump the further the drift.

>>4532896
>with almost the same effective "gravity"
it depends entirely on how they're positioned. If one has a radius of 50m and the other 200km then they're not going to have the same centripetal force. If they're near the same, then they'll have roughly the same force.

>>4532904
(continued)
tl;dr - Jumping directly up will cause you to drift forward on the cylinder. The "higher" your jump the further the drift.

You would also feel coriolis force pushing you to the right.

Actually a problem of Oneill cylinders would be people getting dizzy

>>4532917
>>4532904
Physics without mathematics FTW! lol :P
*pats self on back*

>>4532927
Depends entirely on how big the cylinder is. The bigger the better.

yeah these things are bullshit.


in order for centripetal/centrifugal force/pseudoforce to "push" you back down to the inner surface of the rotating cylinder...

there would need to be a super dense atmosphere that would put a pressure on the surface of your body.


imagine a ring in space (no gravity).


basically, unless you are rigidly connected to the rotating cylinder, you will float away and you will feel absolutely no weight whatsoever.


if you are rigidly connected, such as with magnetic boots or glue...

then you will feel weight.

if you were to disconnect yourself, you would float away (you might tumble for a sec, but you would eventually tumble away).


remember: gravity is what provides objects with the force that pushes them against a rigid surface.

without gravity, you would immediately overcome friction and float away.

>>4532927
>coriolis force pushing you to the right
Define "right".

> a problem of Oneill cylinders would be people getting dizzy
Maybe with very small cylinders, but that shouldn't be a problem with every large cylinders. I believe NASA has done tests and has an estimate minimum size for a rotating space habitat. If my memory serves its slightly smaller than the one from 2001: A Space Odyssey.

>>4532927
>You would also feel coriolis force pushing you to the right.
Wat
Considering you'd be in the rotating frame, as would the cylinder, I'm not sure about that.

>Actually a problem of Oneill cylinders would be people getting dizzy
Maybe if the cylinders were small, but even then only at first. Humans on earth rotate once a day and we're none the worse for it.

So, if the colony were of sufficient size to develop clouds in the center, would the clouds be able to precipitate?

>>4532949
>there would need to be a super dense atmosphere that would put a pressure on the surface of your body.
LOLNO

>>4532952

If you chilling in a rotating cylinder and jump towards the axis you would feela force of value <span class="math">-2m\vec{\omega }\times \vec{v}[/spoiler], basically in the direction perpendicular to your path, either left of right depending what way it is rotating.The magnitude would be small but enough to be noticed in long journeys

people just don't seem to put 2 and 2 together.


lets go back to basic physics, rotating bodies.


the finite/differential elements of a rotating disk or a particle that is undergoing uniform angular motion experiences a centripetal acceleration.


the only reason why that particle or finite element does not fly tangentially away is because it is RIGIDLY connected to the system.


with a rigid body, this is provided by the covalent/ionic/metallic chemical bonds in a bulk material like wood, plastic, or metal.

each particle is rigidly connected to the other particle such that forces are distributed throughout the bulk.


if its a single particle rotating, then the assumption is that it is "held" to a local frame of reference by some force, such as the electrostatic or gravitational force.


but without some force holding that particle to the frame, and without some force holding that particle to the bulk of the rotating object.....

they are simply particles floating around experiencing no attraction whatsoever (for objects the size of space stations, gravity is too weak to be measured).

>>4532963
It depends how fast they were rotating, but probably not. If they were rotating as fast as the ground and no faster? probably not, really. Without much force pulling water out of them they wouldn't shed it at any real speed. If they were going faster then the force would be stronger, and it'd probably work. A stronger force wouldn't be naturally occurant, though.

>>4532963
Yes.

>>4532963
Nope, wouldn't work - the center of the ring is stationary (no "gravity"). Besides, this is a ring - the atmosphere has to be held against the inner surface of the ring (I hope you put up mile-high walls to keep it from spilling out the sides). It's just like swinging a bucket of water around - it's pushed into the bottom of the bucket (edge of the ring) by the rotation (which is maintained by the tensile strength of the ring).

An atmosphere wouldn't stay in the center of the ring anymore than it would stay in one place in vacuum (since that's exactly where it is - in deep space vacuum).

>>4532971


no.


you still don't seem to understand.


that force is provided by gravity.


if there were no gravity, then when you fire a cannon on earth, there would be no coriolis force and the cannon ball would shoot in an absolutely straight trajectory.


>>4532974

imagine we have a big ring and a small ball sitting in space.

both are stationary.

imagine we put the ball really close to , but not touching, the inside surface of the ring and then we begin to spin the ring.


you think that the ball will be attracted to the ring as it starts to spin up?

wow. Great to know that we have discovered a new fundamental force in the universe.

lets get it published before some other 13 year old sci-fi fan does first.

>>4532988
That said, you can have clouds and precipitation in that atmosphere.

It's just that the atmosphere is near the edge of the ring.

>>4532971
Well that's basically what I was arguing here (>>4532904). If you are facing the direction the cylinder is rotating then you would drift "forward" by jumping up and the "higher" you jump the further the drift.

>>4532992

Coriolis force has nothing to do with gravity, its a complementary force that we observe from a rotating reference

also please stop


typing like this

>>4532993
>>4532988
Wait, but we're talking about cylinders, not rings.

I guess you can pressurize the cylinder, but the atmosphere at the center is still going to be a lot thinner than the 1 atm air at the inner surface, especially for a cylinder big enough to avoid dizziness when you jump.

You can have magnetic boots or velcro.


if you stand on the inside of a rotating cylinder or ring, you will be able to stand up, but you will have lots of force at your ankles.


example:

toilet on the space shuttle.


you still have to be strapped down even while its rotating, because your body needs to be rigidly connected to the rotating system.

if you were to unstrap yourself, friction at your ass would be overcome and you would float away from the rotating system.


if you build a space ship, people can walk around with magnets or velcro but they cannot jump. they must always have 1 foot on the ground.


Please think you fucking morons.

>>4532992
You have to spin up everything in the ring along with the ring itself, asshat. That's as dumb as landing on Earth without matching the rotational velocity of the surface first.

>>4533011
I'm calling it: He's a troll.
8/10

>>4532988
The center of the ring has air rotating around with the cylinder. Nothing would stay perfectly in the center for long and anything not perfectly in the center would eventually fall.

>>4533015
Right - the center is an unstable equilibrium, because there is no restoring force. But there's also no force "pushing" you to the edge if you don't have any angular momentum about the cylinder's axis... until you drift into the start of the atmosphere.

As you randomly drift towards an edge and reach the top of the atmosphere, you'll get pushed spinwise by the air rushing past you, and that would cause you to head for the edge even faster. You'd smack into the swiftly-moving "ground" before you matched the rotational velocity though. Air isn't viscous enough for that.

>>4533012


>in the ring

you mean everything rigidly connected to the ring?

the skin on your feet, or the rubber on your shoes does not attract the dirt on the surface of the earth.

the earth's gravity pulls you down.

a big rotating metal cylinder does not pull you down.

if you spun up the ring, everything that wasnt bolted down would slide on the surface and float/tumble away.

you (human beings walking around) need to be bolted down as well.

once again: only sci-fi idiots think that you can have a spinning space ship where everyone is behaving normally like on earth.

no. all you can do is have people standing and carefully walking around so that their bones dont lose density.

very very carefuly running, no jumping whatsoever.

all that you can achieve is the simulation of static weight. standing around experiencing the feeling of a downward force.

>>4533028
>But there's also no force "pushing" you to the edge
Yes there is. The turbulence of the air would eventually push the few atoms of air stuck the very center out of the center. There is an atmosphere in throughout the entire cylinder. It is not a vacuum in the center.

people seem to forget that when you go to an amusement park and you get on the Cyclotron or whatever its called:


1) you sit in a seat with a rubber or foam backing
2) they strap you down
3) they spin it up
4) after it has been spun, the restraints are removed
5) because of FRICTION you are rigidly stuck to the wall (rigid = no net acceleration).


a human who is laying with half of their surface area stuck against a rubber mat experiences tremendous amounts of friction holding them against a surface.


a human standing with only the surface area of the soles of their shoes experiences very limited friction.

without some stronger force holding the human being to the surface, the friction will be overcome by the spin of the object and they will tumble away and be no longer constrained to rotate along with the rigid system.

>>4533040
>you (human beings...
I'm calling it.

>>4533040
>Can't into basic fictional forces(Centrifugal force due to the reference system)
Lrn2physics

I see many words an little math except for one post.

Relative motion is not intuitive at first

>>4533047
For a large enough cylinder, the atmospheric pressure at the center would be negligible. Just like the atmosphere 300 is miles from Earth's surface is negligible. The pressure at the surface of the cylinder comes from the cylinder's rotation, as well as any pressure available at the center. But the bigger the cylinder is, the less of the cylinder's volume would have appreciable atmosphere (if you want ~1g and ~1atm at the cylinder's surface).

And whatever rare gas particles reach the center, they push from all sides (higher pressure at the edges than center). That makes a very weak restoring force to the center, on the net. Probably not significant for any macroscopic object.

>>4533050
>FRICTION

Yeah, he's a troll.

>>4533061
The cylinder would need to be many times larger in radius than the thickness of Earth's atmoshpere because the simulated gravity would diminish more quickly as one approaches the center of the cylinder than gravity diminishes on Earth as one gets further from the Earth's surface. The relatively weak "gravity" in the center of the cylinder would create a huge low pressure zone. I would imagine the cylinder would have to be hundreds of kilometers in diameter to have a practically vacuous space in the center, at which point it wouldn't matter because rain clouds would form well "below" the center of the cylinder in a similar way clouds form within the Earth's atmosphere.

We both can agree that clouds can form O'Neil cylinders, correct?

>>4533110


friction is what prevents objects that are not bolted down or chemically bonded to the rotating object from sliding or tumbling along the inner surface

without friction, the tangential acceleration of every point of the rotating system would cause an object that is not rigidly connected from constantly tumbling along the inner surface in a chaotic fashion.

>>4533061
>And whatever rare gas particles reach the center, they push from all sides (higher pressure at the edges than center). That makes a very weak restoring force to the center, on the net. Probably not significant for any macroscopic object.
The same is true of lighter gasses rising to the top of Earth's atmosphere.

>>4533134
>The cylinder would need to be many times larger in radius than the thickness of Earth's atmoshpere
That's an excellent point. Thanks for helping nail down a point of reference for "how big is big".

And yes, you can absolutely have clouds and rain in O'Neill cylinders. It will just happen in the same atmospheric conditions where it does on Earth - which for large cylinders, is not at the center. The gray area would by cylinders with a radius that is, say, on the order of 20 miles or less, because the differences between the effects of gravity and the cylinder's rotation would change the atmosphere.

Because in Earth's atmosphere, you don't generally have clouds above 5 miles above sea level, I don't think.

>>4533110

the reason that the tumbling or sliding happens is because all of the acceleration/forces associated with rigid body rotation are a function of R.

a particle at R1 experiences a different amount of acceleration as a particle at R2 (different torque as well)

this is also why a rigidly connected body will experience different amounts of stress due to rotational acceleration at different points radially spaced outwards from the axis of rotation.

>>4533146
Once you're already moving at the same angular velocity as the surface of the cylinder there is no friction force needed to keep you "going". The only remaining force is normal to the surface.

>>4533146
>rotating system
>tangential acceleration
I shiggy diggy.

>>4533155
>The gray area would by cylinders with a radius that is, say, on the order of 20 miles or less, because the differences between the effects of gravity and the cylinder's rotation would change the atmosphere.
I believe you are overestimating the necessary space needed for precipitation. You know that NASA building that houses the space shuttle before they roll it out to the launch pad? I've been told it is tall enough that if not for the air conditioning within the building water vapor would precipitate and fall to the floor of the building as rain would.

I believe rain might naturally form within an O'Neil cylinder smaller than 5 miles. I'm not willing to make any guess on what the minimum size would be because there are too many variables: air pressure, temperature, humidity, air circulation, how sunlight or light source is directed, and air composition. If you want to play it safe, I'd suggest bringing an umbrella if you plan on moving to an orbital cylinder even as small as few hundred meters in diameter.

>>4533228
Oh, no, I meant the 5 miles as an upper limit on how far up clouds form at all in Earth's atmosphere, not a lower limit on how big it needs to be for rain at all. You can certainly get clouds much, much lower. Hell, fog is just ground-level clouds.