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| bio | website | |
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| age | ||
| visits | member for | 2 years, 6 months |
| seen | Mar 21 at 12:37 | |
| stats | profile views | 113 |
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Nov 2 |
awarded | Yearling |
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Sep 4 |
comment |
Formula for a ball rolling down an Inclined Plane Yes, I agree. I don't know where the asker got 2/3. Thinking of a disc, maybe? |
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Sep 4 |
comment |
Formula for a ball rolling down an Inclined Plane I = 2/5 mr^2 is for a solid sphere. A basketball full of air is closer to a thin spherical shell (I = 2/3 mr^2) |
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Aug 20 |
comment |
Is Stephen Wolfram's NKS, an attempt to explain the universe with cellular automata, in conflict with Bell's Theorem? @pcr: What's the longest? |
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Aug 16 |
comment |
Tips on teaching Dimensional Analysis? This is just an elementary mechanics problem. To teach dimensional analysis I would suggest perhaps something where you have to convert between systems of units, or maybe a multiple choice question where students have to identify which of a set of unfamiliar equations is correct (where all but one answer can be ruled out due to inconsistent dimensions between the left and right hand sides). |
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Aug 15 |
comment |
pendulum on a rotating table. Will a torque be generated? @NasserM.Abbasi, Yes if I'd seen your edit (mentioning Coriolis forces and Lagrangian dynamics) I would not have assumed I might need to tell you the definition of angular momentum. You never know what level of background one is coming from. :) |
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Aug 15 |
comment |
pendulum on a rotating table. Will a torque be generated? @NasserM.Abbasi, Yes, essentially it's the same as why you can't lift yourself up by your suspenders. As Newton's 3rd law says, as you pull on them they pull back on you in the same amount. But as Adam rightly mentioned, that just means the momentum is conserved, not the velocity. (Angular momentum is angular velocity times moment of inertia, so as the moment of inertia changes (by moving the mass distribution closer or further from the axis) the rotation speed will change. |
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Aug 15 |
comment |
pendulum on a rotating table. Will a torque be generated? +1 I think maybe this is what the asker was really wondering. I focused on the question "Is the angular momentum constant", but of course the angular velocity can change even as angular momentum is conserved. |
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Aug 15 |
revised |
pendulum on a rotating table. Will a torque be generated? added 3 characters in body |
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Aug 15 |
comment |
pendulum on a rotating table. Will a torque be generated? @AdamRedwine, you're right, I should have said "constant angular momentum". I'll edit. |
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Aug 15 |
answered | pendulum on a rotating table. Will a torque be generated? |
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Aug 15 |
comment |
Why does a wobbly metal sheet make the sound of thunder? I suppose I would first want to know if the two sounds are actually similar in terms of waveform analysis. I agree that they sound similar to my ear, but perhaps this is just an artifact of human perception. |
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Aug 15 |
comment |
Does the Pauli exclusion principle instantaneously affect distant electrons? I agree that this could use an edit. e1 and e2 should be electron positions not electrons, but moreover "Suppose the two electrons were exactly the same" is not very clear... do you mean that the two-particle state is a product of two of the same single-electron state? E.g. Psi(x,y) = psi(x)psi(y)? The exclusion principle indicates that such states are forbidden for fermions, whereas psi1(x)psi2(y) - psi2(x)psi1(y) would be allowed. I assume that's what you're getting at, but it's not very clear. |
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Aug 15 |
comment |
A relative time dilation paradox. This is the right answer to the question asked. In the frame of A, B's clock runs slower. In the frame of B, A's clock runs slower. That's not a contradiction. In relativity, time measurements are reference-frame dependent, and we shouldn't expect observers in two different frames to agree. @MarkM's reply addresses the more complicated situation of the twin paradox, where you bring the two twins back together and then ask who's older. That's a good follow up, but goes further than the question that was actually asked. |
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Aug 15 |
comment |
A relative time dilation paradox. In the returning frame, the outgoing twin experienced even more time dilation than the earthbound twin, so switching to this frame provides the necessary correction such that by the time he returns to Earth both twins agree on what their ages should be. |
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Aug 15 |
comment |
A relative time dilation paradox. There are actually resolutions of the twin paradox using just special relativity, pretty much treating the acceleration as happening instantaneously. This works because there are three inertial frames involved (e.g. the earthbound twin, the frame of the traveling twin while he's moving away from Earth, and the frame of the traveling twin while returning to Earth). |
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Aug 15 |
comment |
Why do people rule out local hidden variables? @annav, fair enough, although actually my comment was tongue-in-cheek. 't Hooft is of course a name every physicist knows, but I'm amused to think there may be some younger students reading this thinking "Well, this 't Hooft person only has a few hundred reputation points..." Renormalizing Yang-Mills theory ought to be worth a badge or something. ;) |
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Aug 14 |
answered | A problem of approximation |
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Aug 14 |
comment |
Why do people rule out local hidden variables? On the one hand, @LubošMotl has 43k stackexchange reputation. On the other hand, G. 'tHooft has a Nobel Prize. How am I supposed to know who to believe? Does anyone know the conversion factor? ;) |
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Nov 2 |
awarded | Yearling |
