Interesting Stuff Thread

b318isp · 09-10-2013 12:05pm

Sarky wrote: »

You swing a bucket full of water over your head, the water stays in the bucket. Same principle for people in space.

Is the Coreolis effect (in this case) not the sideways force on a very tall object caused by the rotation of the earth?

sbsquarepants · 09-10-2013 12:08pm

PopePalpatine wrote: »

It's the centripetal effect, which produces a force that is directed at the centre of rotation - much like gravity.

Away from the centre, no?

Sarky wrote: »

You swing a bucket full of water over your head, the water stays in the bucket. Same principle for people in space.

I was thinking along those lines alright, it was the use of the word gravity that threw me!

Sarky · 09-10-2013 12:09pm

b318isp wrote: »

Is the Coreolis effect (in this case) not the sideways force on a very tall object caused by the rotation of the earth?

As far as I remember from my undergrad days, it is. There must be someone here qualified in meteorology/oceanography/physics to explain it, I'm awfully rusty on the principles.

Sulla Felix · 09-10-2013 12:17pm

Yeah, in this case it'd be away from the centre. So, the astronauts would be walking on the inside surface of cylinder.

Reason the coriolis effect comes into play, afaik, the smaller the ship (which would have a higher rpm) the more noticeable the coriolis effect would be.
It acts at right angles from the axis of rotation and when you move away or towards that, you feel a force driving you into the direction of spin. We don't notice it on earth, but it's measurable and the higher the rotation, the worse it gets. Acts on the inner ear to make you dizzy and sick.

swampgas · 09-10-2013 12:19pm

Centripetal - force towards axis of rotation (inwards), centrifugal is the force "outwards". Same thing, just measured in opposite directions.

And there is no difference between the force exerted by gravity and that exerted by spinning a spaceship, they're both just mass experiencing acceleration.

If the spacecraft was attached to (and spinning around) a large mass using a very long tether, I'd guess it would be possible to possible to generate reasonably good "fake gravity".

seamus · 09-10-2013 12:43pm

Sulla Felix wrote: »

Reason the coriolis effect comes into play, afaik, the smaller the ship (which would have a higher rpm) the more noticeable the coriolis effect would be.
It acts at right angles from the axis of rotation and when you move away or towards that, you feel a force driving you into the direction of spin. We don't notice it on earth, but it's measurable and the higher the rotation, the worse it gets. Acts on the inner ear to make you dizzy and sick.

So I'm guessing where the coriolis effect comes into it is the size of the cylinder. A small cylinder needs to rotate more quickly in order to create the same centrifugal force as a large one, thus making the coriolis effect more noticeable. To reduce the coriolis effect while keeping the centrifugal force the same, you need to make the cylinder larger, but then having a huge craft creates its own logistical problems.

I guess to bring this discussion back to where it started, this is the kind of thing that 3D printers and "space docks" let us overcome. Instead of trying to launch a spinning behemoth into orbit, we just fabricate and construct it in orbit.

If Kerbal Space Program has taught me anything, it's that once the craft is in orbit, you don't need very much energy at all to send it to other planets.

swampgas · 09-10-2013 1:45pm

Lots more here: http://en.wikipedia.org/wiki/Artificial_gravity

Obliq · 09-10-2013 2:31pm

Would a massive gyroscope work? Or is it only the spinning part that has gravity? Or does what is inside the space of the spinning part of the gyroscope have this centripetal force on it?

Sulla Felix · 09-10-2013 2:39pm

Obliq wrote: »

Would a massive gyroscope work? Or is it only the spinning part that has gravity? Or does what is inside the space of the spinning part of the gyroscope have this centripetal force on it?

That's pretty much the model, yeah.
Something like this:

If anyone saw Elysium, the space station was just this concept writ large.

url?sa=i&source=images&cd=&cad=rja&docid=x0VMUqgaOCcaKM&tbnid=HYiwL-DheqI25M:&ved=&url=http%3A%2F%2Fstrongphysics.wikispaces.com%2Fch9_hiwf&ei=6FtVUo-XJcGshQetooGwCw&psig=AFQjCNEgtf9QwkPUeKRy0ZNGhQaTuIc-gg&ust=1381412200692197

Obliq · 09-10-2013 2:57pm

COOL! When are they building it?!

But yeah, my question was whether the center of the gyrating object (that stays level, like in a gyroscope) would have that force acting on it - in which case it wouldn't matter how small the craft was as only the outer sphere would be spinning - but I guess not....:o

Didn't do physics. Should have.

swampgas · 09-10-2013 2:57pm

For even larger examples in science fiction, check out Ringworld, or even the Halo rings in the Halo games.

http://en.wikipedia.org/wiki/Ringworld‎
http://en.wikipedia.org/wiki/Halo_(megastructure)‎

Same principle: spin something to create an outward force, indistinguishable from gravity.

Mr. CooL ICE · 09-10-2013 3:16pm

Only time I came across the Coriolis effect was in CoD: Modern Warfare when you had to snipe a guy about 2km away. Basically, when looking through the scope, you could see a slight delay between pulling the trigger and the bullet landing. Because the earth was rotating, the position of the target relative to the crosshair was going to be different by the time it lands, meaning you needed to compensate with the aim.

Sarky · 09-10-2013 3:22pm

swampgas wrote: »

For even larger examples in science fiction, check out Ringworld, or even the Halo rings in the Halo games.

http://en.wikipedia.org/wiki/Ringworld‎
http://en.wikipedia.org/wiki/Halo_(megastructure)‎

Same principle: spin something to create an outward force, indistinguishable from gravity.

Yeah, but Halo is crap. :pac:

I have to admit preference for the Citadel in Mass Effect.

swampgas · 09-10-2013 3:27pm

Obliq wrote: »

But yeah, my question was whether the center of the gyrating object (that stays level, like in a gyroscope) would have that force acting on it - in which case it wouldn't matter how small the craft was as only the outer sphere would be spinning - but I guess not....:o

At the center of a rotating space station there would be zero gravity. As you moved out towards the edge, gravity would appear to increase, and when you reached the outermost part of the station gravity would appear strongest.

It's a bit like standing at the center of a spinning playground roundabout - you're spinning but experiencing no sideways force at the center, but as you move to the edge of the roundabout you feel a stronger and stronger force trying to throw you off.

Also, an easy way to see the coriolis force is to stand on a roundabout facing the center, and swing your leg back and forth - it will move left and right as it swings forward and back.

Coriolis forces are also what cause the rotating winds in the atmosphere, as winds moving towards the poles from the equator (and vice versa) are curled round.

sbsquarepants · 09-10-2013 3:42pm

swampgas wrote: »

And there is no difference between the force exerted by gravity and that exerted by spinning a spaceship, they're both just mass experiencing acceleration. ".

I never thought of it that way, but you're right. I had kind of imagined it as "fake" gravity - doing the same job but not being the same thing, but as you said it's just acceleration doesn't really matter what's causing it.

robindch · 09-10-2013 3:42pm

swampgas wrote: »

Coriolis forces are also what cause the rotating winds in the atmosphere, as winds moving towards the poles from the equator (and vice versa) are curled round.

Coriolis forces are peculiar, but for rotating weirdness, gyroscopis motion is hard to beat:

http://www.thehowandwhy.com/Gyroscopic.html

swampgas · 09-10-2013 3:59pm

Sarky wrote: »

<blasphemy expunged>

I have to admit preference for the Citadel in Mass Effect.

Unintentional pun ??? :pac:

robindch · 09-10-2013 4:01pm

20 libraries which should make you drool:

http://www.independent.co.uk/student/student-life/the-20-most-spellbinding-university-libraries-in-the-world-8778283.html?action=gallery&ino=1

swampgas · 09-10-2013 4:06pm

sbsquarepants wrote: »

I never thought of it that way, but you're right. I had kind of imagined it as "fake" gravity - doing the same job but not being the same thing, but as you said it's just acceleration doesn't really matter what's causing it.

It's known as the Equivalence Principle.

Turtwig · 09-10-2013 4:09pm

Meh,

Best library of them all.
KS-slate-02-lg._V399249911_.jpg

No excessive walking, no heavy lifting, easy access to books and instant dictionary.

Bannasidhe · 09-10-2013 4:10pm

Jernal wrote: »

Meh,

Best library of them all.

No excessive walking, no heavy lifting, easy access to books and instant dictionary.

I love my kindle.

That is all.

James74 · 10-10-2013 3:04pm

swampgas wrote: »

At the center of a rotating space station there would be zero gravity. As you moved out towards the edge, gravity would appear to increase, and when you reached the outermost part of the station gravity would appear strongest.

It's a bit like standing at the center of a spinning playground roundabout - you're spinning but experiencing no sideways force at the center, but as you move to the edge of the roundabout you feel a stronger and stronger force trying to throw you off.

Also, an easy way to see the coriolis force is to stand on a roundabout facing the center, and swing your leg back and forth - it will move left and right as it swings forward and back.

Coriolis forces are also what cause the rotating winds in the atmosphere, as winds moving towards the poles from the equator (and vice versa) are curled round.

My favourite Arthur C. Clarke book Rendezvous with Rama deals with this exact effect. For anybody that hasn't read it I highly recommend it. Great technical details, interesting science but above all a damn good story... and you could polish it off in one sitting.

Cabaal · 11-10-2013 11:01am

Praise be to Lesus!

http://www.bbc.co.uk/news/world-europe-24489512

Vatican pulls papal medal which misspelt name of Jesus

Hotblack Desiato · 11-10-2013 1:27pm

As the inscription is in Latin, shouldn't it have been Iesus not Jesus? I to L is a more common mistaka to maka.

(tuts about declining journalism standards at the BBC...)

recedite · 12-10-2013 11:03am

Not being a latin scholar, I've checked wiki and "Lesus" seems to be the correct version in that language. Interestingly the name Lesus was used throughout the 1611 King James bible.
The original Aramaic name seems to have been Joshua.
In Arabic, Azerbaijani, and in Old Irish its Íosa.
In Finnish its Jeesus.
In modern Irish, Jaysus.