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1914
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age 60
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May
19
comment In which direction does mud fly off a moving bike's tire & why?
At the moment the mud releases, the centripetal force matches the centrifugal force-that is what chooses the moment of release.
May
19
comment Why electric field inside charged conductor is zero in the electrostatic case
You can then apply Gauss' law to a surface just inside the outer surface of the conductor. There is no net charge inside the surface, no electric field inside the conductor, and no surface charge on the inner surface, so no E field inside.
May
19
comment Why electric field inside charged conductor is zero in the electrostatic case
@Algohi: you are approaching this question at the proper level. I would suggest ignoring quantum mechanics and the unit electron charge for this purpose. The point is that the charges in the conductor will distribute themselves so that the internal field is zero. You will get a minus charge next to each positive charge so there is no field going into the conductor. Your are correct that the conductor is neutral, so the positive charge must appear somewhere. It will be spread around the exterior surface in such a way that the field lines hit the conductor perpendicularly.
May
18
comment Why electric field inside charged conductor is zero in the electrostatic case
@JanHudec: This whole calculation ignores both quantum effects and the fact that electrons are indivisible. When we call something a "perfect conductor" we do that. Charges have to be able to move to eliminate the fields inside the conductor. We also don't worry about the thickness of the screening layer. These are all simplifying assumptions that are close enough for many practical purposes.
May
18
comment Why electric field inside charged conductor is zero in the electrostatic case
If the charges are embedded in a conductor, the charges don't matter any more. The conductor is an equipotential with that Q. If it is a spherical shell, the field inside is zero and the field outside is the same as if it were a point charge. If it has a more complicated shape, the field inside is still zero, but you need to solve Poisson's equation outside. Far away, the field will be similar to a point charge. The shape will introduce dipole, quadrupole, etc. moments, but those will die away with higher factors of $r$ than the square.
May
18
comment How hot would tritium water be?
Yes, the total energy gets split between the electron and anti-neutrino. The nucleus takes up the momentum and is so heavy it doesn't take up significant energy. Wikipedia says the total energy is 18.6 keV and the electron averages 5.7 keV-I had guessed it would get half.
May
18
comment How hot would tritium water be?
The energy deposition in the water should be cut in half because there is an anti-neutrino produced which does not deposit its energy in the water. A factor 2 does not change the conclusion much. Good answer.
May
9
comment Both Special and General Relativity carry long term unresolved paradoxes. Should not they now be “inconsistencies”?
There are two senses of paradox. One is a true inconsistency. If that were found, we would invalidate the theory it was found in. The other is a perceived paradox, like the twin paradox in SR. When you analyze it properly, there is no inconsistency, but it can be stated in a way that seems to be a paradox. As far as I know, there are no true inconsistencies in SR or GR. If you believe there is one, you should be specific about stating it and ask how or if it has been resolved.
May
7
comment Both Special and General Relativity carry long term unresolved paradoxes. Should not they now be “inconsistencies”?
Neither of these theories have paradoxes. Both have limits to their applicability. SR only works in inertial frames, but is approximately right if accelerations are small, which they often are. GR works in accelerated frames, and as far as we know it is perfect outside the quantum limit. What paradoxes are you referring to?
May
7
comment Both Special and General Relativity carry long term unresolved paradoxes. Should not they now be “inconsistencies”?
Your title claims that SR has problems, but you don't mention them in the body at all.
May
1
comment If a bell is rung in a perfect vacuum and is suspended by opposing magnets will it ever stop ringing?
You should say that the magnetic force does not act as a damper-the only dissipation is the friction as the objects deform.
May
1
comment If a bell is rung in a perfect vacuum and is suspended by opposing magnets will it ever stop ringing?
You have missed that the only energy dissipation is friction in the distortion of the objects. Without that, the vibration would go on forever.
Apr
30
comment When pressure is exerted on parallel hydraulic pistons, do they start extending at the same time?
@Time4Tea: In a real system there may be a flow restriction, but we have to assume (no info otherwise) that the pressure source can provide all the flow we need to maintain the pressure. It is similar to neglecting friction. In real case friction is there, but in problems like this we say it is negligible. The same for pressure drops.
Apr
12
comment Is fuelless aviation possible?
The more specific you make your question, the better the answers you are likely to get. No, you can't fly solely on gravity because it pulls down. Both answers (and the link you give) are using buoyancy to counteract gravity.
Apr
6
comment Why does the bathroom become hot after a bath?
If the drops were already water, moving them to the walls won't generate any heat. True, if you cause vapor that was in the bath to condense you will. I don't see why shower water would cause this.
Feb
25
comment Paradox in electrostatics in relation to Gaussian surfaces?
You are claiming that if your first holds true there is no flux out the non-common faces because the total flux is zero. Logically, that is correct, as a false antecedent makes an implication true. I don't think that is useful. Then we know the flux integrated over a sphere is proportional to the charge within it. If the flux through the other five faces were zero, the flux through the common face would reflect the charge inside the cube, but it isn't so you can't make that argument.
Feb
25
comment Is possible carry light using a rectangular mirroned tube?
There are several vague ideas linked together in this question. Certainly one can make a rectangular box with mirrored walls which will transmit light. Why one would want to do this for a telescope is speculation. Why calculus has anything to do with it is hard to figure. Vote to close as unclear what you are asking.
Feb
23
comment Instead of a dynamo-meter, why can't we use $\tau=I\alpha$ to determine the power of a rotating shaft?
The MOI of the shaft will remain the same, but there might be coils attached that are spinning as well. Computing their MOI may be hard. Whether or not the motor attains steady state before something falls apart depends on the motor and setup. Yes, you can measure acceleration during that period. I didn't say it cannot be done, I suggested some practical difficulties that I think will mean the data is not as accurate as with a dynamometer. In some cases yours will be a good approach.
Feb
21
comment What are the coordinates of the center of rotation of our galaxy, relative to ourselves?
You can't put up a signpost fixed to the Earth's surface that points to these locations. You can identify a point relative to the stars that points to these locations, or any other outside the solar system. Have you gone outside at night and noticed that the stars you see change from day to day and hour to hour?
Feb
18
comment How can we count 17 particles in the standard model
Why do you think there are specifically $17$? I think the normal count is six quarks in three colors (18), their antiquarks (18), six leptons, six antileptons, eight gluons, photon, W$^\pm$, Z, Higgs for a total of $60$