beansbaxter
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posted May 23, 2004 01:41 PM
Give me your best physics questions
Hey give me your best physic questions please...it's raining here in Pullman, and I'm just not in the mood to ride until it warms up a lil more...besides the playoff game starts in a few hours...
So yeah, give me some good physics-related questions I can ponder over...please.
   
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worm~hole
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posted May 23, 2004 01:50 PM
 Edited By: worm~hole on 23 May 2004 14:52
how does your sphincter muscle know when to taper it off? 
____________
“We sleep safe in our beds because rough men
stand ready in the night to visit violence on those
who would do us harm.”
-George Orwell
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trenace
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posted May 23, 2004 03:26 PM
1) What factors are required to predict neutron capture cross section?
2) Is there much energy barrier to a neutron approaching a nucleus?
3) Do free neutrons end up in nuclei according to the "probability of finding" them in that spacial location; is this relevant at all, is it alone sufficient basis for predicting neutron capture, if not why not?
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worm~hole
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posted May 23, 2004 03:41 PM
...please calculate the mass and gas ball size of Uranus...
____________
“We sleep safe in our beds because rough men
stand ready in the night to visit violence on those
who would do us harm.”
-George Orwell
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beansbaxter
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posted May 23, 2004 06:08 PM
quote:
1) What factors are required to predict neutron capture cross section?
2) Is there much energy barrier to a neutron approaching a nucleus?
3) Do free neutrons end up in nuclei according to the "probability of finding" them in that spacial location; is this relevant at all, is it alone sufficient basis for predicting neutron capture, if not why not?
1) This is a difficult question to answer. I can give you factors, but you probably won't be able to do much with them as this is QCD which is VERY difficult to do. You would need to know:
i) the incoming and outgoing 4-momenta of all particles
ii) the coupling constant (probably just -i g(sub s) for the first level tree diagram, and then more for the higher order diagrams
iii) some other mathematics involving the propagator (gluons), balancing energy and momentum, and then some more math
You'll end up with an expression involving the matrix element of the reaction, or the amplitude for this process to occur. Once you have that, you have to square it, multiply it by a whole ton of other stuff, and then you can get the cross section. It's not fun.
You can also get the matrix element directly by drawing the feynmann diagram for the process, but as it involves a number of quarks in each neutron and a whole ton in the nucleus, I would really not recommend doing this unless you really want to do a few hundred (thousand?) integrals.
2) There isn't any energy barrier AFAIK. That's why neutrons are so useful for imaging nuclei. (search for work done by Bertram Neville Brockhouse... nobel prize for neutron work).
3) I would say so yes. As the strong force acts on short distance scales the expectation value of r for the neutron would matter here.
(I guess the simple answer to 1 would be you would need to know the momentum/energy of the nucleus and neutron, their trajectories, and the "strength" of the strong force... that's as basic as it'll get I guess. If you want to actually calculate numbers, you'll need some QCD)
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beansbaxter
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posted May 23, 2004 06:11 PM
quote:
how does your sphincter muscle know when to taper it off?
I always figured it just did it to keep your butt from slapping shut. If it didn't it would sound like someone "golf clapping" when you had diarrhea.
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worm~hole
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posted May 23, 2004 06:26 PM
...wow...you're good...kids tell'ya!...the future of America is in good hands
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“We sleep safe in our beds because rough men
stand ready in the night to visit violence on those
who would do us harm.”
-George Orwell
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trenace
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posted May 23, 2004 07:31 PM
Edited By: trenace on 23 May 2004 20:37
Thanks beansbaxter, that was of some help in understanding.
Nope, I can't do QCD calculations. My skills barely extended to graduate quantum chemistry and I mean barely (since I did not know linear algebra going in, the homework sets alone took me 20 hrs a week, which I did NOT have as this was only a totally-unnecessary elective taken for fun...)
I didn't expect that it is as simple as the "probability of finding" the neutron there, trajectories, and momenta of the nuclei and neutrons, as values vary enormously between nuclei with little apparent correlation to anything (in my amateur examination of the matter) except for mass defect relative to the isotope formed, and even that not so predictive. E.g., gadolinium 157 has a truly enormous value. It would have to take more detailed methods such as you discuss.
Not that I have to be able to do it and I won't be able to...You just wanted a physics question and that has been one that has puzzled me since I was a teenager, but never remotely had the skills to really ever approach working out an answer to...
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Michael Lee
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posted May 23, 2004 07:36 PM
If a R1 leaves the house at 8:00am and a 10R leaves the same house at 8:15am, how long would it take the 10R to put the wooop asssszzz on the R1. Bikes have equal mods but the 10R rider is 8lbs heavier?
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frEEk
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ummm... yeah
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posted May 23, 2004 09:04 PM
damn beans, yer smarter than u look!
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ZXLNT
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posted May 24, 2004 04:43 AM
Is a singularity neccessisarily a single point??
And if so, shouldn't all black holes be the same size even though mass may vary???
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EastBayDave
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posted May 24, 2004 04:58 AM
is warp 10 possible? 
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Enjoy the ride!
02' ZRX1200
00' ZX12R sold
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zzzzzxxxxxr12
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posted May 24, 2004 05:01 AM
If first is last, and last is first, where does it begin and where does it end?
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worm~hole
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posted May 24, 2004 06:19 AM
...and what if Pluto got close to Uranus...what then?
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“We sleep safe in our beds because rough men
stand ready in the night to visit violence on those
who would do us harm.”
-George Orwell
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swft
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posted May 24, 2004 06:38 AM
Explain entropy. 
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your car is slow
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Fuck Nitrous...Got Boost?
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posted May 24, 2004 07:01 AM
Why do Harry, TurboBlew, and MattSterbator all sit to pee?
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Do not taunt happy fun ball!
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matt sterbator
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posted May 24, 2004 07:44 AM
quote:
Why do Harry, TurboBlew, and MattSterbator all sit to pee?
To make sure you don't miss a drop 
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Some day, you're going to run out of some days
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beansbaxter
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posted May 24, 2004 07:53 AM
Edited By: beansbaxter on 24 May 2004 11:15
quote:
Is a singularity neccessisarily a single point??
And if so, shouldn't all black holes be the same size even though mass may vary???
When we talk about the size of a black hole people generally refer to its gravity well, or more specifically where the event horizon is (the point where even light cannot escape). Oddly enough the more massive a black hole is the smaller this area is.
I should also add that of course, it is all theory, for no one has visited a black hole yet.
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beansbaxter
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posted May 24, 2004 08:17 AM
Edited By: beansbaxter on 24 May 2004 09:51
quote:
Explain entropy.
Haha, I should have known coming from you. Yeah, I don't think you could ever find a good explanation for entropy. It is one of those concepts that are well defined mathematically but still almost impossible to grasp. Entropy is usually described as "the amount of disorder in the system", and that isnt even a good description but it is probably the best one you can get.
In a perfect world, any system would be perfectly reversible. Meaning you could go from point A to point B back and forth as long as you like. However, in practice some amount of energy is always lost as heat. This is called entrophy. Eventually, entrophy will reach a point where the whole universe is the same temperature and as a result no work can be done.
Thermodynamics is without doubt the most difficult field in classical physics. Personally, I think quantum mechanism is easier to understand.
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BA
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posted May 24, 2004 08:48 AM
what's this business I've read about controlling the spin of the electron, and how/to what do they intend to apply this if it works?
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beansbaxter
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posted May 24, 2004 08:53 AM
quote:
how does your sphincter muscle know when to taper it off?
I thought about it some more, and there also must be some sort of adaptive closed loop servo system because it also has to handle gas flow as well as perform a check valve operation to keep you from sinking while swimming. I think I said that right.
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worm~hole
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posted May 24, 2004 09:45 AM
Edited By: worm~hole on 24 May 2004 10:47
entropy(sic): is it a measure of the unavailable energy in a closed thermodynamic system that is also usually considered to be a measure of the system's disorder and that is a property of the system's state and is related to it in such a manner that a reversible change in heat in the system produces a change in the measure which varies directly with the heat change and inversely with the absolute temperature at which the change takes place?...or as the beans essentially stated: the degradation of the matter and energy in the universe to an ultimate state of inert uniformity?...does it apply to quantum mechanics of the sphincter muscles and how it controls exit of mass and gas, too?
____________
“We sleep safe in our beds because rough men
stand ready in the night to visit violence on those
who would do us harm.”
-George Orwell
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beansbaxter
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posted May 24, 2004 10:13 AM
quote:
Yeah, I don't think you could ever find a good explanation for entropy. It is one of those concepts that are well defined mathematically but still almost impossible to grasp. Entropy is usually described as "the amount of disorder in the system", and that isnt even a good description but it is probably the best one you can get.
Dang, now I kinda want to retract that statement, because basically there are two driving forces in the world, (1)the drive to go from higher energy to lower energy and (2)the drive to go from order to disorder. All chemical reactions hinge on these two effects.
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beansbaxter
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posted May 24, 2004 10:45 AM
quote:
what's this business I've read about controlling the spin of the electron, and how/to what do they intend to apply this if it works?
Uh oh, this one kinda has me stumped...see you can control spin by applying an external magnetic field. In fact, materials that are ferromagnetic are so because all the spins (each spin being the total spin of an ion) are poinging in the same direction.
So we have been controlling spins for a long time. I dont know how "they" intend to apply it though?
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wannabe
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posted May 24, 2004 11:43 AM
Here's one: what does a cat in a box have to do with quantum mechanics?
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