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• Users: Vaal
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1. ### Viscosity and Drag

When you point out the mathematics I guess it does make sense. I don't have a lot of dynamics experience and I guess I am just having trouble intuitively getting used to the idea that the number of interactions (which is proportional to the density) would not change the viscosity. Thanks for...
2. ### Viscosity and Drag

The article I linked may have not been the best example, I think it is referring to the force at terminal velocity (notice that a general v is no were in the expression). Classical Mechanics by Taylor explicitly says drag force is b*v and in problem 2.2 says b is given by 3pi*n*D where d is...
3. ### Viscosity and Drag

I am talking about the case of linear drag (small Reynold's number). http://en.wikipedia.org/wiki/Stokes%27_law
4. ### Viscosity and Drag

The linear drag coefficient is a function only of object size and medium viscosity. Multiply sources say viscosity of air is independent of pressure and density. How can the linear drag be independent of density of the medium? It seems like less dense medium should mean fewer collision and in...
5. ### Fractal Behavior

The data is a scalar value for all points in a 2D plane. I am most interested in seeing if patterns that are evident on large scales repeat themselves on smaller scales, like is seen in fractals. I'm interested in both 1D and 2D patterns. Thanks.
6. ### Fractal Behavior

Hi, I have been looking for fractal behavior in a data set. I've used the box method to determine fractal dimension by looking at the inverse of box size and the number of boxes needed to enclose the object. These two variables seem to be fairly accurately predicted by a power law...
7. ### Rayleigh Scattering and Density

I disagree, the sky you see up high is being viewed through a large amount of low altitude air and thus would be tinted blue regardless. In a similar fashion you can in fact see scattering directly in front of you but the distances are typical too short for any appreciable effects. This isn't...
8. ### Rayleigh Scattering and Density

Equation 9a in this paper is one of many sources...
9. ### Rayleigh Scattering and Density

This is what I was inclined to believe at first too but at STP the mean distance between air molecules is around 4nm, 100 times less than the wavelength of visible light. Also, in Intro to Optics Hect specifically talks about air and implies that this is true for Rayleigh in the atmosphere. Is...
10. ### Rayleigh Scattering and Density

So I have become a bit confused by the relationship between intensity of Rayleigh scattering and density of the gas. Multiple sources (ex. Salby, Atmospheric Physics) give the scattering cross section per molecule, σ, to be dependent on 1/λ4, the index of refraction of the material and 1/N2...
11. ### Uncertainty of an Operator

Yeah, I thought that might be that case but I wasn't sure. Thanks. The two definitely are pretty much equivalent, I just wasn't quite seeing how so, thanks again.
12. ### Uncertainty of an Operator

\Delta\Omega2=<\Psi|(\Omega - <\Omega>)2|\Psi> (hope that is legible) but I'm confused as to how the middle, (\Omega -<\Omega>) is defined. Isn't this an operator minus a scalar? I know I can also find \Delta\Omega2 by summing the the products of the probabilities of all the states...
13. ### Uncertainty of an Operator

Given the state and an operator I know the uncertainty of this operator can be calculated via (see next post latex is being weird, sorry)
14. ### Latent Heat of Fusion and Potential Energy

Andrew, thanks for the reply. I hadn't considered compression causing potential energy to turn into thermal energy that seems like it is on the right track. The one aspect of this theory I don't quite get though comes from the fact that the problem asks for the maximum possible height. With the...
15. ### Latent Heat of Fusion and Potential Energy

I was looking over an old qualifying exam and I came across a problem asking what the maximum height of a mountain on Earth could be. The solution states that the rock at the base of the mountain will melt and flow away when the potential energy of the top layer of the mountain is equal to the...
16. ### Time-reversal invariance and irreversibilities

saim, The behavior, on the microscopic level, of most thermodynamic systems is effectively random. As a result of this some macroscopic states of the system are drastically more likely than others, this arises more so out of the math than physics. So it is possible for all thermodynamic systems...
17. ### Quantized Energy Levels

If you solve Schrodinger's equation for a particle in a box you find the solutions to be sines and cosines. The boundary condition that the wave function must go to zero at the edges of the box then leads to the need for an integral number of wavelengths and in turn quantization of energy. I...
18. ### Particle in a box momentum uncertainty

Ok, I think I figured out the first part described above, although I can't seem to make the numbers come out right. I am lost on the next problem, even more so than the last. My well currently has walls at +/- a and a particle is in the ground state. the walls are suddenly moved to +/- b...
19. ### Particle in a box momentum uncertainty

1. this is for a particle in a box (infinite potential well): For the wave functions calculate (as a function of n) \Deltax \Deltap \Deltax\Deltap Homework Equations h = h bar below u+n(x)=(1/\sqrt{a} )cos((n-1/2)(pi)x/a) u-n(x)=(1/sqrt{a})sin(n(pi)x/a) E-n=h2/(2m)(n(pi)/a)2...
20. ### Forced question

For (i) you will have three basic forces acting on the skier: gravity, the pull from the rope they are holding and the force of the water on there feet. (b) is getting at the fact that the skier is at a constant velocity therefore the forces must be in equilibrium according to Newton's first...
21. ### Distance between planet and vessel - Trig problem

The easiest way to figure out the length of s would probably be to use the law of cosines, a good description of which can be found here: http://mathworld.wolfram.com/LawofCosines.html
22. ### Polynomial Proof

If you don't think its needed I won't bother with it. Thanks again for all your help.
23. ### Polynomial Proof

After a little more thought I realized my formula for fm(x) could be better obtained by the formulation for repeated use of the power rule, (di/dxi) xk=k!/(k-i)! xk-i where i \leq k, rather than "extrapolate the pattern". I'm still at a loss for a better way to express the content of the...
24. ### Polynomial Proof

Thank you both, that helped a lot. I actually thought about taking successive derivatives before but for some reason the fact that all the derivatives would be zero for all x didn't occur to me at the time. Here is what I have so far, I ended up not really using induction so please let me know...
25. ### Polynomial Proof

Homework Statement Prove that if a0+a1x+a2x2+a3x3+...+anxn=0 then a0=0, a1=0 ... an=0 Homework Equations none The Attempt at a Solution I think I can do this for n up to 2 in the following way (please tell me if you see any gaps in my logic here): f(x)=a0+a1x+a2x2=0 (from the...
26. ### Curve Sketching

That is a good question. The second derivative test actually will not work on critical values that lie on the very edge of the original function's domain(i.e. the point where x=0 in this case). From the graph of the original function you can see x=0 is the highest point point in the neighborhood...
27. ### Block on Ramp

For 1 I would say in practice yes, the frictional force that you are interested in does change if the block changes direction. For 2 the is answer is basically yes. You are right that you need to check to see if static friction is small enough that the block will slide back down but in...
28. ### Curve Sketching

With the exception of a one small issue in part e ("x > 0 or x > 1" should just be x > 1) you have everything correct including your derivatives. You can find the max and min values with the critical points you have from part e, x=0 and x=1, in the manner that you specified above. Just a heads...
29. ### Testing GRE Physics Subject Test

Thats good to know, I was a little worried it might put me at a huge disadvantage not to submit it but it sounds like that isn't the case. I had no idea the correlation was that poor. Its also great to hear from someone else coming from a smaller school who has done well in grad school. I think...
30. ### Testing GRE Physics Subject Test

I have been trying to figure out whether I should submit my physics subject test score to grad schools if it is optional. I scored a 29 percentile on the test which despite being relatively high for my school doesn't look great on a grad school app. 'm not applying to any really top schools but...
31. ### Grad School Subject Test and Research Interests

I feel the same way in that I don't want to close doors by becoming to set on anyone topic now, but it seems that most of the grad school applications want you to specifically state your research interests. From what you say though it sounds like it does not really hurt you to say you aren't...
32. ### Grad School Subject Test and Research Interests

I am looking to go to grad school for applied physics next fall. I'm applying to mostly mid grade schools (University of Virginia, University of Maryland at Baltimore County as well as a few smaller ones) and I had two questions: First off, I came from a small liberal arts school where GRE...
33. ### Conservation of Momentum of a spring

a) you have the formula right you just need to plug in the correct values and solve. We can say: m1=m, the mass of the block m2=M, the mass of the box v1=0, they are assumed to be still to start with v2=0, again they are not moving to start u1=v1, the problem says the block's velocity is...
34. ### Total mass of the earth's atmosphere

One kPa is a kN/m2. That means that for every m2 of the Earth's surface there must be 100kN of atmospheric weight. Convert this force into mass using F=ma (the atmosphere is thin enough that you can assume a=9.8m/s2 for its entirety and still get a reasonably accurate answer) and then multiply...
35. ### Grad School and Field

No, I hadn't even thought about that. I have been looking for something with an interdisciplinary component which medical physics certainly has. I will definitely look into it further.
36. ### Grad School and Field

I'm about to apply grad school and I'm trying to get an idea of the field I would like to go into within physics. I'm pretty good with theory but I really prefer hands on work. I would also like to specialize in a topic in which it is easy to find research work that is not related to defense...
37. ### Spring & Projectiles

Yep, it is a little hard to tell with the formating but it looks like you got it for the most part. It might just be a formating thing but the only thing I'm not following is the minus sign before the last square root symbol.
38. ### Physics Applications

I think that is definitely a cool idea. I really liked Gravitation 2.0. I thought Vad(http://www.soulfox.com/flash/vad.php) was really cool too. Were you thinking of something kind of like Vad except with a few more features, a few more numbers on the side and maybe a little more control...
39. ### Work and Potentential Energy of a Spring

Problem a asks for the work done by gravity, which is a downward force. Since the object is lifted up the direction of the force is opposite the direction of the motion, which leads to negative work or -39.2J in this context. The same idea is true for c. The spring is exerting a force toward its...
40. ### Spring & Projectiles

I am pretty sure I see what you're getting at but I think there might be a few typos in your post so I may be wrong. You are on the right track so far, but double check your equation for V. I think you might have left out a squared/square root. Also, you seemed to have swapped the h with a y...