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comment Why are position and velocity enough for prediction and acceleration is unnecessary?
@isarandi the key difference here is that in the sense you used it, "model" and "law of physics" aren't distinguishable! That's not to say there aren't deeper reasons physics.stackexchange.com/questions/18588/…
Dec
19
comment Is imaginary time a fifth dimension?
@KyleKanos You're right, but there's imaginary time in a different sense that Hawking introduced. No idea what it is though, beyond SR I'm just speaking in buzz words. edit I think it's this different since OP is talking about since he's talking about 3+1+1 quantities.
Dec
19
comment Is imaginary time a fifth dimension?
@KyleKanos en.wikipedia.org/wiki/Euclidean_quantum_gravity en.wikipedia.org/wiki/Imaginary_time All i know, solely from Hawking's "My Brief History", is that imaginary time (in a sense beyond special relativity) is related to Euclidean quantum gravity.
Dec
18
comment Questioning Einstein's view on gravity
During the development of relativity, you didn't have "quanta" of light. What you did have are Maxwell's equations, for which constant magnetic fields, constant electric fields, and EM waves are all consequences of the same framework. So it doesn't matter if you can't imagine how to test photons being massless. What matters is verifying the correctness of Maxwell's equations. THEN you come up with a frame transformation that leaves Maxwell's equations satisfied and voila, special relativity.
Dec
11
comment Is the kinetic energy of an electron always $1.6 \cdot 10^{-19}~\text{J}$?
I think your description of where you're stuck is insufficient.
Dec
9
comment Minimum angular velocity for circular motion (pendulum)
@Wolphramjonny great! But now your equation contradicts your sentence "There is no such minimun agngular speed" (meaning, what if $g/L\omega^2>1$?)
Dec
4
comment How does an operator transform under time reversal?
Also, for reference \langle and \rangle produce nice looking brackets, $\langle \varphi | \psi \rangle$ instead of $< \varphi | \psi >$, if you care about that sort of thing.
Dec
1
comment Disk and Ball on a smooth surface
@Samurai You were right! My mistake was thinking the $mA$ term (in MathGod's post) didn't matter.
Nov
30
comment Disk and Ball on a smooth surface
@Samurai just checking, this isn't a Lagrangian mechanics question is it?
Nov
29
comment Alternative type energy storage to batteries?
Fun fact: I believe that the tokamak reactor at General Atomics San Diego uses flywheel power storage (at an off-site facility), since it can't just draw the massive amounts of power it needs directly from the grid.
Nov
29
comment Maxwell's Inspiration to think about fields
I think this answer takes that one sentence of the question too literally? Yes there are atoms, but there are also fields with a reality/effect of their own, and that's a big switch from saying that there are atoms with some instantaneous action at a distance force.
Nov
26
comment What do people actually mean by “rolling without slipping”?
@Muphrid I think I will. But come to think of it, that the center of the disk travels $2 \pi/9$ is perfectly expected, so maybe the statement is true if "travels one circumference" refers to the center of the disk.
Nov
26
comment What do people actually mean by “rolling without slipping”?
(with "s" being the arc length movement of the point of contact with the curve)
Nov
26
comment What do people actually mean by “rolling without slipping”?
@Muphrid I included the overall distance travelled by the point of contact! I'm just looking at rolling without slipping on curved surfaces and many online solutions write $r d\theta=ds$, but I'm pretty sure (citing my example above) the correct version is $rd\theta=(1-kr)ds$, where $k$ is the curvature of the surface. Actually I derived that formula using the "a point in contact with the ground is momentarily stationary" condition. I'm mostly posting this for a sanity check.
Nov
26
comment What do people actually mean by “rolling without slipping”?
@Muphrid, see: mathandcode.com/img/diskrollnoslip.gif would you agree that this example shows that your bolded sentence isn't true on non-flat surfaces? It illustrates a circle radius $8/9$ rolling inside a circle radius $1$. The circle rolls an angle of $2\pi/8$ while its point of contact with the ground travels a distance $2\pi$ and the center of the circle travels a distance $2\pi/9$ (not $2\pi/8$).
Nov
26
comment Why is cross section inversely proportional to wavelength for interstellar scattering?
Hookean springs have $F\propto x$, though $x$ and $F$ are different units. The unit conversion is introduced in the constant of proportionality $k$. $F=kx$.
Nov
24
comment Do bad clocks measure proper time?
Could you copy the definition of good versus bad "in the sense of MTW §1.5"?
Nov
22
comment How does a giant walk-in fridge maintain a thin temperature gradient at the entrance?
@WetSavannaAnimalakaRodVance Thanks for that!
Nov
21
comment How does a giant walk-in fridge maintain a thin temperature gradient at the entrance?
Is there a wind curtain? (A box/rail above the door which blows a wall of air down. They're present at many store entrances)
Nov
20
comment What is the physics of a spinning coin?
related: physics.stackexchange.com/questions/68676/… and mathandcode.com/disk I wanted to solve this problem in full generality. So my solution is undoubtedly more complicated than it needs to be. But you should be especially interested in "Partial constraint 2"