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Physics Help and Math Help - Physics Forums - www.physicsforums.com | Site profile
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Posting activity table on Physics Help and Math Help - Physics Forums:
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3 Months
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3,754
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39,772
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118,603
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Physics Help and Math Help - Physics Forums posting activity graph:
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Top authors on Physics Help and Math Help - Physics Forums during last week:
user's latest post:
solving problem l'Hospital...
Published (2009-11-19 21:26:00)
In fact, the limit in your last problem is 1/2,not 0, so sorry to burst your bubble. You don't need L'Hopital's Rule for this problem. Factor x^2 out of the two terms in the radical, and bring it out of the radical as x. In the next-to-last step you can cancel the x in the numerator with the x in the denominator, leaving you with 1 in the numerator and and expression that approaches 2 in the denominator. For #1, you're...
user's latest post:
Impact Force vs. Weight
Published (2009-11-19 23:54:00)
Easiest way is conservation of energy. When you are up in the air, potential energy = mass * g * height change Moving this becomes kinetic energy (don't worry about this) Because when you are stopped at the bottom all of this KE has become spring energy = 1/2 k X^2 Where k is the spring stiffness and X is the compression of the spring. So simply: m g h = 1/2 k x^2 if you don't have 'k' for the spring (it's not going...
user's latest post:
Re: Acellerating expansion? Bah!
Published (2009-11-19 15:15:00)
Originally Posted by Chalnoth The supernova community is very much interested in these issues, and they're continuing to work on them. There really isn't a problem there. Yup, but there is always room for more people in the party. I'm a somewhat inactive member of the supernova community. One thing that I'd really like to do is to start pushing out some of the theoretical codes that are out, because I think there may be...
user's latest post:
Re: Need help understanding the...
Published (2009-11-19 23:22:00)
Originally Posted by JesseM But during the period twin2 is accelerating, twin1 is moving inertially, so isn't that section of twin1's worldline already included in t', which is supposed to be the proper time in twin1's inertial phase? Or are you defining t' to be only the proper time along the section of twin1's worldline where twin1 is moving inertially and twin2 is not simultaneously (according to the...
user's latest post:
Re: Need help understanding the...
Published (2009-11-19 23:09:00)
Originally Posted by cfrogue The equation c/a sinh(aBT/c) would be the elapsed proper time experienced by twin1 for the acceleration of twin2. But during the period twin2 is accelerating, twin1 is moving inertially, so isn't that section of twin1's worldline already included in t', which is supposed to be the proper time of twin1's inertial phase? Or are you defining t' to be only the proper time along the section of...
user's latest post:
Charge consumed by a circuit
Published (2009-11-19 19:30:00)
Here is a circuit simulation of the above IR receiver. Input current from IR diode: 800 microamp pulse (red), right scale. 9 volt pulse (black) on transistor collector output, left scale. The relay turns ON when collector drops below about 1 volt, and OFF when the collector rises above about 5 volts. Bob S
user's latest post:
Help me to find the article, please
Published (2009-11-19 19:19:00)
Hi limarodessa! Welcome to PF! It seems to have been specially written for that book (translated into English by Kip S Thorne), and not published anywhere else. The book's publisher was W H Freeman (ISBN 0-7167-0337-8). Perhaps the original Russian version was published in some Russian-language journal?
user's latest post:
Momentum "Broken...
Published (2009-11-19 23:56:00)
Take the components m1v1 and m2v2 along x and y-axis. As you can see from the figure, net x components is zero and net y component is equal to m3v3. You have two equations and two unknowns. Now solve foe m1 and m2.
user's latest post:
Solar radius of a star
Published (2009-11-17 01:40:00)
The star's luminosity should be 2.7*10^31 W, not 2.7*10^32 W. With the correct luminosity, you get 23 solar radii, very close to Wikipedia's figure.
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Top 10 active forums on Physics Help and Math Help - Physics Forums during last week:
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Top 10 forums on Physics Help and Math Help - Physics Forums:
General Discussion
- 190,991 posts
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Academic & Career Guidance
- 97,112 posts
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Politics and World Affairs
- 85,018 posts
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Special & General Relativity
- 76,886 posts
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Introductory Physics
- 70,635 posts
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Quantum Physics
- 66,965 posts
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General Physics
- 61,396 posts
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Calculus & Beyond
- 57,335 posts
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General Math
- 50,382 posts
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Philosophy
- 47,626 posts
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Latest active threads on Physics Help and Math Help - Physics Forums:
Started 19 hours, 17 minutes ago (2009-11-20 21:02:00)
by mgb_phys
neutrinos go through the earth easily
only a very small percentage of them are stopped by the rock
they aren't trapped as such - they are absorbed by an atom and have an effect, changing the atom
Started 2 days, 8 hours ago (2009-11-19 08:14:00)
by cabraham
The b-e voltage is at roughly 0.7V, but the 0.2V you refer to is the c-e voltage. The b-c voltage is the difference, or 0.5V. The base is at higher potential than collector and emitter. The current in the base is the holes injected from base to emitter, plus the electrons injected from emitter to base which do not reach the collector, plus the holes injected into the collector, as well as ...
Started 1 month, 1 week ago (2009-10-09 19:57:00)
by CFDFEAGURU
Could you post this version of Faraday's Law?
Thanks
Matt
Started 1 day, 23 hours ago (2009-11-19 16:37:00)
by bpet
Originally Posted by kingwinner
... for the case of CONTINUOUS random variables?
Even then it's tricky - try some examples first with X1 iid X2 and then with X1=X2 and you'll see how those ...
Started 2 days, 20 hours ago (2009-11-18 19:28:00)
by leroyjenkens
I think you underestimate the potential for damage. As well as underestimating the deterrent factor for even a little damage.
Animals also seem to be naturally scared of fire, even without getting hurt by it.
2] ...
Started 1 day, 5 hours ago (2009-11-20 11:14:00)
by sokrates
Heisenberg Picture = States are constant, Operators are evolving
Schrodinger Picture = Operators are constant, states are evolving
Their difference = Semantic.
I don't think this is a serious problem either for Kubo or for Keldysh. As for the initial equilibrium assumption, doesn't hurt anything because these are steady state equations anyway. So you can take t--> inf. before you do ...
Started 1 year, 8 months ago (2008-03-09 20:02:00)
by DaveC426913
Originally Posted by K.J.Healey
ALL stars should have some orbital radii where liquid water could exist, correct? Its not just surface temp but gravity, other gaseous atmosphere to keep it non vaporous, etc....
Started 19 hours, 25 minutes ago (2009-11-20 20:54:00)
by xxChrisxx
Welcome.
What is the formula for kinetic energy? Why do you think it will have less?
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Hot threads for last week on Physics Help and Math Help - Physics Forums:
Started 1 week ago (2009-11-14 10:24:00)
by Doc Al
Originally Posted by matheinste
Reading up on Bell's standard spaceship paradox in wiki and other places, I see quite a heated argument and some physicists being accused of some basic misunderstandings. To cut a long story short, one of the ...
Started 1 week ago (2009-11-14 12:15:00)
by Janus
There are three factors that have to be considered when dealing with the Twin paradox: Time dilation, length contraction and the Relativity of simultaneity.
As far as A in concerned, he can consider B as the one moving, and from his measurement it is B that undergoes time dilation. But also, the distance between B and the turnaround point undergoes length contraction.
So for example, ...
Started 1 week, 2 days ago (2009-11-12 13:34:00)
by dx
The principle of relativity applies to the laws of motion, not the motions themselves. Obviously, the spacetime motion of an electron or an EM field is not lorentz invariant, i.e. it does not look the same in all frames. What does look the same is the law of motion , i.e. Maxwell's theory. Instantaneous action, by definition, has to refer to a special hyperplane of simultaneity, and therefore ...
Started 1 year, 8 months ago (2008-03-19 20:06:00)
by P4PPY
A maximum of 2 senses can be active at a time during a dream. In reality you can use all of your senses at once. :)
Hey... what?... it sounds really really good!
Started 1 week, 3 days ago (2009-11-10 16:57:00)
by meopemuk
Originally Posted by DarMM
Yes, the Hamiltonian is not a well-defined finite operator on Fock space, but in most QFTs it can be shown to be a well-defined finite operator on another Hilbert space. Do you view this as a problem?...
Started 2 days, 9 hours ago (2009-11-19 06:22:00)
by cristo
Wow! I don't know which part I'm more surprised about, that the mother called the police in the first place, or that the police officer tasered the child. Either way, if I was the father, I'd be lobbying for sole custody immediately!
Started 5 days, 23 hours ago (2009-11-15 16:32:00)
by JesseM
Originally Posted by cfrogue
Can anyone answer this?
GPS satellites are preprogrammed before launch due to relativistic effects mainly time dilation and gravity.
Yet, once in orbit, the satellite should view the earth frame as "...
Started 6 days, 14 hours ago (2009-11-15 01:25:00)
by Sorry!
Originally Posted by Equate
real life in India? Is this it?
Does it, the movie, Slumdog depict the sentiments in India?
I know there are quite a few Indian people frequenting this board, so please chime in and clarify some ...
Started 1 week ago (2009-11-14 14:22:00)
by hellbike
And what is more important to you, doing what you love, or achieving certaing targets?
Started 6 days, 22 hours ago (2009-11-14 17:39:00)
by Andre
Congratulations, Pythogrean.
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