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re: Edinburgh/MIT scientists to announce evidence for life in Venus’ atmosphere
Posted on 9/15/20 at 8:40 pm to Kentucker
Posted on 9/15/20 at 8:40 pm to Kentucker
quote:
Simple thought experiment: You’re floating in space in a giant circular spaceship tube that’s 5 kilometers in diameter overall with the tube itself being 50 meters wall-to-wall inside it (because a tube essentially has only one wall, let’s call the walls 1. Above you; 2. Below you; 3. Right of you; and, 4. Left of you. There are no divisions of the tube so nothing can hit you as the circle turns. The circular tube starts to turn. Faster and faster while you continue to float equidistant to the walls.
You contend that the spinning tube will generate a centripetal force or a centrifugal force to pull or push you to a wall within the tube. Centripetal means moving or tending to move towards a center. Centrifugal means moving or tending to move away from a center. These two forces are easy to understand when using earth-based examples. What happens in the microgravity of space?
Wait... what?
That’s not at all how a centrifuge is expected to work for simulation of gravity. You don’t just sit in the middle of the drum and watch it spin around you. Here’s how your thought experiment should work:
In your same example of a tube, you strap yourself into a chair on the “outer wall” of the tube (the “roof” and “walls” don’t matter, as the outer wall is the “floor”). The tube starts to turn. Since you used the example of a 50 km diameter, it only has to turn at about 0.14 rpm to get “up to speed”. Once it’s turning at 0.14 rpm, you unbuckle you’re seatbelt and stand up. The ring is no longer accelerating. Just spinning at 0.14 rpm.
Since you are in 3D space it’s kind of hard to explain the centripetal acceleration that follows. But let’s use a compass rose for simplicity:
Remember your head is pointed at the middle of the compass rose with your feet pointed outwards. Let’s say the compass rose is rotating clockwise. If you unbuckle your seatbelt and stand up just as you pass the north arrow, you are moving “east” at about 733 m/s. Since you can’t continue to move “east” past the outer wall of the ring, your direction must change. By the time you pass the east arrow, you are moving “south”. By the time you pass the south arrow, you are moving “west”. The net result is that the floor is constantly forcing you to accelerate towards the center of the ring at roughly 9.8 m/s^2 - centripetal acceleration - which leads to an apparent centrifugal force roughly equivalent to gravity on earth.
The long and short of it being that the spinning tube on its own doesn’t generate shite. It’s the interaction between you and the tube once you’re both spinning that simulates gravity. It sounds like you may be way overthinking this. Despite your previous reply about Einstein’s theories, it’s Newtonian physics. In fact, it’s really just a combination of the three laws of motion.
There are some complications - for example the Coriolis effect. But it has nothing to do with gravitational fields or relativity. It’s just acceleration.
ETA:
Should have just started with a gif..
I’m a little surprised someone can have even a basic understanding of relativity without understanding centripetal acceleration in a centrifuge. This is a fairly basic physics problem that you would encounter in high school physics, as well as multiple times in any type of engineering program.
This post was edited on 9/15/20 at 9:00 pm
2
Posted on 9/15/20 at 8:53 pm to Kentucker
quote:Where did I insult you?
Sorry you are resorting to insults. You must feel defeated. More discussion with you would be a waste of time. Good night.
And yes, I do tend to feel defeated when someone continually rejects very simple concepts. I just feel like it would be a shame if you left without realizing your misconception.
I THINK I UNDERSTAND WHY YOU ARE SO CONFUSED.
You think that centrifuges need earth's gravity to work. You keep bringing up general relativity. You think centrifuges somehow warp spacetime and create or manipulate gravity. THAT'S NOT HOW THEY WORK.
A centrifuge only works by putting its contents into motion, typically via friction. The contents tend to want to travel in a straight line, which results in the centrifugal force away from the center of rotation. The walls of the centrifuge prevent the contents from escaping, this is the centripetal force toward the center of rotation. The two forces balance, holding the contents against the walls. These are the only forces at play. Any gravitational effects are irrelevant, neither desired nor necessary.
Posted on 9/15/20 at 8:58 pm to lostinbr
quote:
The net result is that the floor is constantly forcing you to accelerate towards the center of the ring at roughly 9.8 m/s^2 - centripetal acceleration - which leads to an apparent centrifugal force roughly equivalent to gravity on earth.
Once you unbuckle from the chair, there’s nothing to keep you from pushing off the wall. You are moving at the same speed as the wall, after all. The gravitational relationship between you and the wall is identical to the relationship before you and the wall started moving. If you come into contact with the wall you won’t “stick” to it in a gravity-like situation.
Posted on 9/15/20 at 9:07 pm to Kentucker
quote:
Once you unbuckle from the chair, there’s nothing to keep you from pushing off the wall.
You mean other than your inertia, which is always tangential to the ring?
quote:
You are moving at the same speed as the wall, after all. The gravitational relationship between you and the wall is identical to the relationship before you and the wall started moving. If you come into contact with the wall you won’t “stick” to it in a gravity-like situation.
The acceleration isn’t due to a change in speed. It’s due to a change in direction. You can’t move in a circle without your direction of travel changing. Your direction of travel can’t change without acceleration. You can’t accelerate without a force. This is basic physics.
Posted on 9/15/20 at 9:10 pm to Kentucker
quote:
You are moving at the same speed as the wall, after all.
Are you under the impression that if the wall were to suddenly disappear, you would keep spinning around in a circle...as if the wall were still there. I really don’t understand How you don’t get this...
Posted on 9/15/20 at 9:12 pm to lostinbr
quote:
I’m a little surprised someone can have even a basic understanding of relativity without understanding centripetal acceleration in a centrifuge. This is a fairly basic physics problem that you would encounter in high school physics, as well as multiple times in any type of engineering program.
It’s equally surprising that no attempts have been made to build a rotating ring for the ISS, considering how simple you think the concept is. It’s obvious to those of us who are in Einstein’s camp regarding gravity, however.
The debate is active, but the artificial gravity camp seems to be in the majority and will no doubt push for an expensive addition to the ISS to be constructed. The proof will be in the construction, to paraphrase an old axiom. We’ll see.
Posted on 9/15/20 at 9:13 pm to Kentucker
quote:Yes there is, your body's inertia.
Once you unbuckle from the chair, there’s nothing to keep you from pushing off the wall.
quote:The wall is rotating about the center of mass, your body is trying to fly in a straight line.
You are moving at the same speed as the wall, after all.
quote:There is no gravitational relationship (aside from the minuscule gravitational attraction between them, which is irrelevant here).
The gravitational relationship between you and the wall is identical to the relationship before you and the wall started moving.
quote:But you will "stick" to it in the sense that you are constantly flying toward it while pushing away from it with your feet.
If you come into contact with the wall you won’t “stick” to it in a gravity-like situation.
This post was edited on 9/15/20 at 9:36 pm
Posted on 9/15/20 at 9:21 pm to Kentucker
quote:The concept is simple, the construction at a meaningful scale is not.
It’s equally surprising that no attempts have been made to build a rotating ring for the ISS, considering how simple you think the concept is.
quote:
It’s obvious to those of us who are in Einstein’s camp regarding gravity, however.
Again, we aren't talking about gravity.
quote:
The debate is active, but the artificial gravity camp seems to be in the majority and will no doubt push for an expensive addition to the ISS to be constructed. The proof will be in the construction, to paraphrase an old axiom. We’ll see.
It likely won't happen because the cost would far exceed the benefit, assuming they don't dream up some specific experiment that requires simulated gravity. Astronauts don't spend enough time up there for the lack of gravity to do them much harm. And the convenience of having simulated gravity would be far outweighed by other uses of the same amount/cost of material.
The only way a centrifugal artificial gravity ship would be built is if we reach the point that we want to send humans to other star systems. Other than that, there's no point.
General relativity has nothing to do with it.
Posted on 9/15/20 at 9:29 pm to Korkstand
quote:
The only way a centrifugal artificial gravity ship would be built is if we reach the point that we want to send humans to other star systems. Other than that, there's no point.
Even a mission to Jupiter/Galilean moons? That would be a hike.
Posted on 9/15/20 at 9:33 pm to Sun God
quote:I can't imagine sending humans out there for research when robots can do that. I also can't imagine colonizing anything that far from the sun. The only way I see humans going out that far would be if we make space travel much faster, in which case artificial gravity still wouldn't be necessary.
Even a mission to Jupiter/Galilean moons? That would be a hike.
Of course I could be totally wrong or overlooking something, but I just don't think the economics of a giant rotating space ship will make sense until we are ready for interstellar travel.
Posted on 9/15/20 at 9:34 pm to Kentucker
quote:
It’s equally surprising that no attempts have been made to build a rotating ring for the ISS, considering how simple you think the concept is.
Interesting you should bring this up.
1. Scientists use centrifuges for experiments on the ISS all the time. Here’s an article from NASA describing one of the centrifuge test platforms. Remember, you said centrifuges don’t work in microgravity:
quote:
Because gravity determines so much of a live organism’s behavior and growth, centrifuge-based experiments have long been a part of biological investigations in space. While the pull of Earth’s gravity makes this type of investigation difficult at home, the space station’s microgravity environment makes it the perfect place for fractional gravity experimentation. MVP greatly expands that testing capability for the space station.
“This is a permanent, commercially owned research facility that gives researchers the opportunity to study the effects of gravity and partial gravity on living organisms, and, hopefully, by extrapolation to humans,” said Rich Boling of Techshot, the company responsible for MVP’s design and build.
What makes the facility so special is its size and capability. Containing two carousels that spin quickly to simulate up to two times the force of gravity, the platform is the largest centrifuge in the U.S. segment of the space station and allows investigators more room for, and control over, their research.
2. The primary reasons the ISS hasn’t added a spinning module for accommodations are, first, that it’s a fairly expensive addition, and second, that the entire point of running experiments in space is to take advantage of the lack of gravity. Still, there have been multiple proposals by multiple space agencies to do so. I can link them if you’d like, though I already referenced NASA’s Nautilus-X concept for long range space flight earlier in this thread.
quote:
It’s obvious to those of us who are in Einstein’s camp regarding gravity, however.
Who is “us”? Where is the credible physicist you’re referencing that claims you can’t generate centripetal acceleration in space? It’s not Einstein.
quote:
The debate is active
No, it’s not.
Sure, there are active questions (being researched by NASA) around the health effects of artificial gravity produced by a centrifuge. Primarily questions around how it affects the inner ear. But nobody other than you is arguing that centrifuges don’t work in space.
Posted on 9/15/20 at 9:37 pm to Korkstand
Good point 
Posted on 9/15/20 at 9:37 pm to cgrand
quote:
/MIT scientists
quote:
“teaming with life”.
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