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  • 0 posts edited
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  • 22 votes cast
Mar
29
comment Flywheel energy storage: Why not use room temperature diamagnets instead of superconductors?
It could very well be viable in spacecraft though (I think there is ongoing research on diamagnetic bearings).
Mar
29
comment Flywheel energy storage: Why not use room temperature diamagnets instead of superconductors?
@WilliamBudd I've been looking into this lately and I've come to the conclusion that the diamagnetism effect is probably not strong enough. I don't have exact numbers, but if you consider that a piece of bismuth can barely stabilize a ~ 1 gram neodymium magnet (very strong magnetic field) with the help of a lifter maget, we're talking about restoring forces on the order of <1 millinewton. You could probably stabilize a very light "flywheel" with this, but real flywheels weigh at least a few tons, any amount of systematic vibration or gyroscopic effect will run your shaft into the diamagnets.
Mar
22
comment Stabilizing a shaft with only one electromagnet
@CuriousOne I didn't think Earnshaw's theorem applied to a dynamic electromagnet... I was not able to find affordable small magnetic bearings, all I could find was company websites requiring asking for quotes (meaning it's in the tens of thousands of dollars), could you share a link in case I am missing a keyword?
Mar
22
asked Stabilizing a shaft with only one electromagnet
Mar
9
awarded  Popular Question
Feb
16
awarded  Enthusiast
Nov
3
comment What is the speed of the fastest moving body in our solar system?
@ThomasPornin I would imagine it doesn't make much difference to the final speed, though, as most of the speed is gained as the comet falls deep into the Sun's gravity well (the last few hundred thousand kilometres), though I have no proof besides playing KSP to back that up. So the comet must have entered our system with an escape velocity considerably higher than the Sun's escape velocity (at which point it is questionable whether it really is "in" the solar system as it will either quickly escape or collide with something).
Sep
24
awarded  Autobiographer
Jul
10
comment Why is it necessary for an object to have a bigger size than the wavelength of light in order for us to see it?
last link is dead
Feb
26
comment Why is the moment of inertia (wrt. the center) for a hollow sphere higher than a solid sphere (with same radius and mass)?
@user130632 Never mind.
Feb
26
comment Why is the moment of inertia (wrt. the center) for a hollow sphere higher than a solid sphere (with same radius and mass)?
This isn't rigorous, you haven't defined "low" and "high" and the scale of the gradient!
Nov
29
comment Would a sneeze by a cosmonaut in a spacesuit affect his movement?
So does that mean we can design sneeze-propelled engines?
Nov
28
comment Photons from stars--how do they fill in such large angular distances?
@JonofAllTrades I don't think gregsan was talking about that property of the laser, but just referring to any ordinary object that emits light into a cone rather than radiating outwards in every direction (a laser pointer comes to mind..) but the explanation would be valid even for a flashlight (barring atmospheric scattering effects, of course)
Nov
28
comment Photons from stars--how do they fill in such large angular distances?
A quick safety note: please do not stare into laser beams.
Aug
16
comment Information Preservation and Burning Books
@sundar From a theoretical point of view, if the laws of physics are reversible then your scenario cannot happen, since reversibility would imply that if two initial states $A$ and $B$ lead to the same state $C$, then $A$ and $B$ must be the same. Otherwise you couldn't really "reverse" that particular state, could you? Though on a practical level, yes, for us mere mortals, as we do not have the ability to reverse the laws of physics to see in the past, that information is as good as lost to us. This assumes the laws of physics are indeed reversible, of course.
Jul
15
comment How can you weigh your own head in an accurate way?
@MichaelBrown Ah I see, that is quite nice. I think I'll go with the suit though, otherwise I might not have enough mass for those satellites to get a stable orbit :p
Jul
14
comment How can you weigh your own head in an accurate way?
Won't the equipment and space suit skew the results?
Jul
14
comment How can you weigh your own head in an accurate way?
I think you broke his neck.. interesting approach though +1
Jul
14
comment How can you weigh your own head in an accurate way?
"The Compton scattering measurement is done by scanning your head with a gamma ray beam" sounds safe enough, you try first.
Jul
13
comment Where does the light go when I turn off the light switch?
Where does it go when you leave the light on? Surely it doesn't build up? That should answer your question :)