# Search results

1. ### Mass of an Object

The math shows the theoretical distributions of mass, not necessary to be physically possible for any power of 1/r. So it's really a matter of discussing what actual densities are possible. You also asked to give a physical explanation to a seemingly math confusion, so you may want to specify...

yes
3. ### Crash Courses in Physics Topics?

Thanks! I cannot seem to find quantum mechanics or lagrangian mechanics anywhere though?
4. ### Crash Courses in Physics Topics?

Does anyone know of any "crash courses" in various physics topics such as classical mechanics, quantum mechanics, theories of relativity, field theories, etc free online? By "crash courses" I mean PDF's for example with good examples, since I learn the quickest with examples. I know it is rather...
5. ### Schrodinger Equation, Potential

wow... thank you. This is just what I thought, and I still heard it as potential.
6. ### Schrodinger Equation, Potential

Schrodinger Equation, "Potential" This is a very simple question, but I am confused. I have seen Potential and Potential Energy interchanged.. yet still referred to as potential. Is the "potential" function in the schrodinger equation really a potential function or potential energy? (units...
7. ### Temperature vs Heat

In terms of Kelvins, if the temperature of a sample doubles, does the energy content from heat double as well? Also, if you are passing a current through a sample, what should be the temperature vs current relation be theoretically? i.e. what is f(I) in T = f(I). Thanks,
8. ### Help my dad and I settle a argument

So if the question is about where on the arm to stand to lower the lift faster, then I agree with you, you apply the same force downward. In fact, standing on the end will give more torque like you said and may squeeze the arm against the vertical part causing more friction and may make it even...
9. ### Relative energy of simple 2 particle system (confused )

..this isn't a physics homework question.. just a wonder of mine
10. ### Relative energy of simple 2 particle system (confused )

Relative energy of simple 2 particle system (confused!) Ok so I have a simple question which I feel I should know the answer to: Setup: Two particles of different mass.. say M and m (where M > m) are moving past each other by some constant velocity. If we view the energy of the system from...
11. ### Quantum Mechanics - Leonard Susskind on Integration by Parts

Right ok thanks, I lost my mind there a little bit!
12. ### Quantum Mechanics - Leonard Susskind on Integration by Parts

He mentioned something about boundary conditions, could you explain to me what you mean? What boundary conditions could make the term vanish?
13. ### Quantum Mechanics - Leonard Susskind on Integration by Parts

I'm watching the video series on Quantum Mechanics taught by Leonard Susskind, (from Stanford). On Lecture #3, Dr. Susskind says that integration by parts is: ∫FG' = -∫GF' However from what I know integral by parts to be, there i missing a +FG on the righthand side, or something... since I...
14. ### Linear functions/operators conflicting understanding

So in my theoretical physics class my professor was reminding us ("reminding") of what "linear" means, such as a linear functions or a linear operator. He said the definition was: 1. f(ax) = a f(x) 2. f(x + y) = f(x) + f(y) Functions or operators are "linear" if they meet the above 2...
15. ### ODE, bernoulli equation -> leads to crazy integral !

thanks very much! jonny
16. ### ODE, bernoulli equation -> leads to crazy integral !

ehild, thank you! How do you know to do that substitution? thanks again, Jonny
17. ### ODE, bernoulli equation -> leads to crazy integral !

But how could I get it even in terms of the integral? I need a constant of integration to solve for so y(1) = 1/2
18. ### ODE, bernoulli equation -> leads to crazy integral !

ODE, bernoulli equation --> leads to crazy integral ! Homework Statement An Initial Value Problem, ODE (Bernoulli equation) ODE: [x^2]*y' + 2*[x^3]*y = [y^2]*(1+2*[x^2]) IV: y(1) = 1/2 Homework Equations general form of Bernoulli's equation: y' + a(x)y = b(x)*[y^n] First...
19. ### Simple ODE problem, Bernoulli's Equation

k thanks ill do that
20. ### Simple ODE problem, Bernoulli's Equation

Well it turns out I forgot how to multiply both sides of an equation. 3rd to last step I multiply half of the right side by t^2, I'm not sure how to make this thread "solved."
21. ### Simple ODE problem, Bernoulli's Equation

[SOLVED] simple ODE problem, Bernoulli's Equation Homework Statement Initial value problem: Relation: t*y' - 2*[t^2]*sqrt(y) = 4*y Initial value: y(1) = 4 Homework Equations general form of Bernoulli's equation: y' + a(t)y = b(t)*[y^n] First order, linear ODE form: y'...
22. ### Integral of 1/x = ln(x) Problem has missing absolute value?

My solution is that, it is an Initial value problem, (there is only one t which we care about) and with that t the argument in the natural log is positive and so u can ignore the abs value!
23. ### Integral of 1/x = ln(x) Problem has missing absolute value?

Integral of 1/x = ln(x)... Problem has missing absolute value!? This is an ODE problem and solution, but what I'm not understanding here is calculus based: Why does the argument to the red-boxed ln() not in absolute value signs?? ( | | ) u = cos(t) so the numerator can be negative. I am just...
24. ### Programs Changed major to physics

I switched my major to physics from Electrical Engineering, (I am finished with freshman year and will be starting sophomore year as physics major), and many people seem disappointed with the decision. I think it has mainly to do with how much money is made; physics vs. engineering. I have to...
25. ### A very good video on quantum mechanics

In the fourth video of that series, he says space and time are quantized. I thought that wasn't fully accepted yet? Am I wrong or if not, where is evidence that Planck time and distance are really the shortest?
26. ### 10^(trillion) years from now

congratulations!
27. ### 10^(trillion) years from now

Interesting, I was though asking specifically 10^1,000,000,000,000 years from now.
28. ### If wormholes connect two areas in spacetime, wouldn't that require 5

Nabeshin, that is what I understood from the first couple of posts and I realize I just need to study General Relativity to understand curvature fully.
29. ### If wormholes connect two areas in spacetime, wouldn't that require 5

The paper is supposed to be 2d, that is the point. The real fact that it is 3d, (has thickness) is irrelevant. Then your saying our spacetime has thickness in some 5 dimensions?? EDIT: I should say, the fact that a real piece of paper is 3d is irrelevant, because it's not really a piece of...

Okay.
31. ### If wormholes connect two areas in spacetime, wouldn't that require 5

My original question is: How can there be imaginable wormholes connecting two points in our 4d spacetime without an extra 5th dimension. The paper analogy is a 2d spacetime, connected were imagining a 3rd dimension to bend the paper into. If your saying that we never introduced a third...
32. ### If wormholes connect two areas in spacetime, wouldn't that require 5

dude, 2d spacetime connecting 2 points through 3rd dimension. There isn't a 3rd dimension in 2d spacetime... Are you saying there is 5th dimension in our 4d spacetime? I'm asking if that's the case.
33. ### If wormholes connect two areas in spacetime, wouldn't that require 5

your analogy doesn't have the same dimensions as reality, if it did why would u call it an analogy?
34. ### If wormholes connect two areas in spacetime, wouldn't that require 5

But your example is connecting two points in 2d spacetime isn't it, there is not 3rd dimension supposedly, yet you used it to connect the two points.
35. ### If wormholes connect two areas in spacetime, wouldn't that require 5

If there didn't exist a 3rd dimension you would not be able to fold them and connect the points.
36. ### If wormholes connect two areas in spacetime, wouldn't that require 5

Ok well, I find that to be crazy. So can it then be thought of as, scaling? For instance instead of imagining the x-axis bend into the y direction in some regions, can by the same way imagine the x-axis scaled differently at those "bent" regions?
37. ### If wormholes connect two areas in spacetime, wouldn't that require 5

If wormholes connect two areas in spacetime, wouldn't that require 5 dimensions? (an extra dimension past 4d spacetime.)
38. ### The Blue Forehead Room Problem

Yeah, but how does the process work when you see 3 other blues, (and you yourself are blue.)
39. ### The Blue Forehead Room Problem

But what information can possible be obtained after the first night?
40. ### The Blue Forehead Room Problem

Well what do you think of what I said.
41. ### The Blue Forehead Room Problem

Summary is below, here are the original videos. (Also, in case this problem has been posted before, you can show me the link, I could not find it.) The Original Problem: http://www.youtube.com/watch?v=rBaCDC52NOY" The Solution: http://www.youtube.com/watch?v=-xYkTJFbuM0" (I have a...
42. ### GR in all frames of reference

Also, is there a connection between Frame-Dragging and inertia?
43. ### GR in all frames of reference

but that bothers me you said: "The laws of physics are the same in both coordinate systems." Then how are centrifugal forces explained in the "rotating" frame?
44. ### GR in all frames of reference

A very important idea in General Relativity is, same laws in all reference frames. How does that work in rotating reference frames? Jonny
45. ### 5th fundamental force?

[Neutrinos] are not composed of quarks and therefore don't have a strong interaction. If you want to know why they don't collide due to gravity (lol) look https://www.physicsforums.com/showthread.php?t=406212". EDIT: I'M SORRY, I THOUGHT YOU SAID NEUTRINOS, NEUTRONS are composed of quarks...
46. ### 5th fundamental force?

Well, you have the electromagnet force repelling them, and the strong force keeping them together. I once wondered why the nucleus doesn't explode from all the electromagnetic repulsion (all the protons in the nucleus are positively charged) but the explanation is the strong force keeps them...
47. ### Time, and thermodynamics

Ok thanks, I subject I will be studying not too far from now.
48. ### Time, and thermodynamics

Ok so I am asking two things here. One is, if entropy supposedly always increases, how does that fit with the big bang? The highly dense ball of all matter in the universe mashed together in the beginning seems to have high entropy; where is the organization?? Second, why does it seem time...
49. ### Singularity & Actual Infinites

Yeah that is just what I thought! Very interesting physics!
50. ### Singularity & Actual Infinites

Actually I wonder the same. I believed infinites only exists in concept, but now you remind me of how a black hole has infinite density. Any more knowledgeable comments on this?