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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 $60$
Feb
18
comment What happens when a high speed motor tries to drive a heavy car? High torque?
Torque being too high is shown by excessive acceleration (maybe you bump into things before you can steer) or by wheels slipping. It sounds like you are thinking the motor has a fixed torque output, but for a robot (or a car) you usually have some control over it like a throttle. If the gear ratio is low enough that you can make so much torque that the wheels spin, you just don't use so much throttle. Also if the gear ratio is that low you will hit max speed (where there is no torque) very quickly.
Jan
27
comment Throwing an object around the Earth. Is it possible?
@Alex: true, not all ellipses pass through the ground, but we know the launch point is on the ground. If you want to use the altitude of the height of Obelix and launch due horizontal, the ellipse can avoid contact with the ground. Otherwise it will pass through the earth. Orbital rockets avoid this by getting up above the atmosphere, then being thrown fast enough to stay in orbit.
Jan
27
comment Throwing an object around the Earth. Is it possible?
@JavierBadia: that is the point of Joshua's answer, and a very good one. +1
Jan
27
comment Throwing an object around the Earth. Is it possible?
You are spot on. A pity the accepted answer missed this. In theory the javelin could reconfigure itself as it is out of the atmosphere from minimum drag to a lifting body, but I think this is out of the spirit of the question.
Jan
21
comment What enables protons to give new properties to an atom every time one is added?
@Sofia: to get multicharacter superscripts, put them in braces. So ^{12}C gives $^{12}C$
Jan
10
comment Can asteroids fall on earth and hit the surface at 90 degree angle?
@LDC3: The point is that the solid angle around an altitude of 90 degrees is very small. I agree it was unclear, so I edited.
Jan
4
comment Why do the errors in a formula depend on how it's written?
Normally when you quote errors as percent, what you are quoting is relative error. So a $3\%$ error in $R$ means $\frac {\Delta R}R=0.03,$ not $\Delta R=0.03$ You can do the analysis with fixed errors, but that is not common.
Dec
23
comment Can someone please explain the forces acting on the rod?
It will get closed instantly on physics unless you show some effort.
Dec
14
comment How can we be Certain that Dark Matter Exists if we Cannot See it or Directly Detect It?
Have you read Wikipedia ? There is a long section on the observational evidence.
Dec
13
comment What's the physical interpretation of an arbitrary normal mode for masses and springs?
Yes, the common frequency is where the eigenstuff comes from. You assume that each mass moves with a common frequency, but its own amplitude and phase. Then $\ddot x_i= \omega^2 x_i$ , you get $(A-\omega^2)\vec{x}=0$ and you want nontrivial solutions.
Dec
6
comment How Earth's Gravity is more powerful than its centrifugal force?
This line of reasoning allows the earth to spin more slowly (reducing the centrifugal force to near zero) but sets an upper limit to how fast it can spin. What would be the length of a day if the centrifugal force at the equator equaled $g$? In that case, if you ran East, you would launch into orbit.
Dec
4
comment Lagging in induction coils
I think you have something in mind that I am not understanding. The inductor resists changes in the current instantly. It certainly does not make bigger current spikes. If we just connect the circuit across the supply with no inductor, the current instantly goes to steady state when we connect the supply. The inductor will make it ramp up with a time constant $L/R$. We can't say what would ruin the circuit without knowing what that circuit is.
Nov
14
comment How come Wifi signals can go through walls, and bodies, by kitchen-microwaves only penetrate a few centimeters through absorbing surfaces?
@user3237992: the difference is that microwave ovens and WiFi operate at essentially the same frequency, so changes in absorption due to frequency are off topic here. I believe they penetrate the same, but we care about WiFi penetration and we don't recognize that the oven microwaves penetrate just the same.
Nov
14
comment How come Wifi signals can go through walls, and bodies, by kitchen-microwaves only penetrate a few centimeters through absorbing surfaces?
@K7PEH: It looks like your comments are directed to OP, not to me. You can comment on the question for that.
Nov
13
comment How come Wifi signals can go through walls, and bodies, by kitchen-microwaves only penetrate a few centimeters through absorbing surfaces?
@K7PEH: I don't expect the attenuation is any different. I said that a few times. The oven wall provides enough attenuation that we don't care about the signal (just as power) any more, then attenuation through walls knocks it even lower.