23,937 reputation
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bio website lightandmatter.com
location Fullerton, California
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visits member for 3 years, 3 months
seen 7 hours ago

I teach physics at Fullerton College, a community college in Southern California. I have an undergrad degree in math and physics from Berkeley and a PhD in physics from Yale. Back when I was doing research, my field was experimental low-energy nuclear physics.


7h
revised Producing photons with same frequency, different amplitude wave
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7h
answered Producing photons with same frequency, different amplitude wave
7h
comment Producing photons with same frequency, different amplitude wave
If you insist on thinking of photons as waves (which is fine of course), you can think of all of their amplitudes as being equal. Not true. If you think their amplitudes are all the same, what do you think it is?
7h
comment Producing photons with same frequency, different amplitude wave
This doesn't answer the question.
7h
comment Producing photons with same frequency, different amplitude wave
Two photons of the same frequency have the same "amplitude", No, their wavefunctions can differ.
7h
comment Why aren't we Boltzmann brains in an infinite universe?
What makes you think I'm not a Boltzmann brain? I'm offended at your non-inclusive language.
8h
comment Is there any physical quantity that does not have uncertainty?
@CarlWitthoft: The uncertainty principle does not apply to counting the number of items (even photons). There is an uncertainty relation between number of quanta and phase for a harmonic oscillator: physics.stackexchange.com/questions/67929/…
8h
comment Is there any physical quantity that does not have uncertainty?
The OP is asking about quantum uncertainty, which is qualitatively different from uncertainty in measurements in general.
8h
revised Underdetermined forces in a statics problem
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comment Underdetermined forces in a statics problem
@dmckee: Even a small deviation will break the symmetry and make the system determined again. Hmm...I sketched an analysis, and it didn't look that way to me. In the asymmetric case, it seems to me that you have four unknowns ($N_1$, $N_2$, $F_1$, and $F_2$), and three equations: $F_x=0$, $F_y=0$, and $\tau=0$.
9h
comment Underdetermined forces in a statics problem
Friction only affects the cylinder sliding. Unclear. Rolling is affected by rolling resitance. True, but I don't see how it's relevant. Even with an infinite μ a cylinder can still roll easily. True but irrelevant. As long as the cylinder can roll, friction will not support a static load because the cylinder will still roll. Unclear.
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awarded  Nice Question
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comment Underdetermined forces in a statics problem
I don't understand your comment above. Some of your statements seem true, some false, and some unclear.
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comment Underdetermined forces in a statics problem
Hmm...there are a lot of statements in your answer for which you haven't offered any reason, and that I'm not convinced are true. Friction will not support any static load from the cylinder. E.g., I don't think I believe this statement. In any case friction should play no role [...] This would cease to be true if the angle between the planes was less than 90 degrees. Clearly friction would play a role for $\theta=0$. Do you have a reason why you believe that the behavior is qualitatively different for $\theta<90$ deg?
13h
comment Underdetermined forces in a statics problem
@BMS: Yes, but in that example it's clear why it's underdetermined, and how the system knows what solution to pick: it picks the solution that's imposed by the externally determined force on the rope. Here there doesn't seem to be any such external force presently being exerted on the system that could determine which solution to pick.
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comment Underdetermined forces in a statics problem
@ja72: I don't think your analysis is right. The problem is underdetermined for any value of $\mu>0$.
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revised Increasing matter density in the Friedman equations?
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comment Underdetermined forces in a statics problem
@Michal: No need to apologize for trying to help! If you like, you can delete your answer.
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comment Underdetermined forces in a statics problem
Note that the equation is an inequality, so it doesn't actually determine the frictional force, it only limits it to a certain range.
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answered Increasing matter density in the Friedman equations?