Ponder Stibbons
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Why does a liquid not rotate with the container?
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54 votes

Suppose your cup was full of a lump of stuff that had no friction. Then as you rotate your cup there is no force between the cup and the stuff, and so it would not rotate. In the case of coffee - the ...

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Why can't the Schrödinger equation be solved exactly for multi-electron atoms? Does some solution exist even in principle?
16 votes

The problem is not at all unique to Schrödinger's equation, it is a common feature of differential equations. The same thing happens all over the place in classical electro-magnetics. But, also to say ...

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Why isn't average speed defined as the magnitude of average velocity?
16 votes

Given a velocity as a function of time, the speed as a function of time is the magnitude of the velocity at each point in time. The average speed is then the average of this magnitude, as it would be ...

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Does Special Relativity Imply Multiple Realities?
12 votes

Relax, take a deep breath :-) to me it seems that you do not realise that Alice and Bob have two different times. That is, what Alice calls time, Bob calls a mixture of space and time. So, If you ...

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Does electric charge vary between observers?
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5 votes

The core of the issue is the determination of inertial frames, where an inertial frame is defined as being a frame in which the laws of mechanics are the same. But, which laws? If it is Newtonian ...

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Standing wave is transverse but can it also occurs in longitudinal wave?
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5 votes

Sorry, that was a bit terse. http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/tralon.html#c1 Look at the diagram in the link. The point of a longitudinal standing wave is that a region of ...

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When an object crosses a black hole event horizon, does the entire object cross the event horizon "all at once?"
4 votes

As you approach the event horizon, from the point of view of an external observer your head approach your feet. You become shorter and shorter. But, this process takes an infinite amount of time. You ...

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If electrons can be created and destroyed, then why can't charges be created or destroyed?
4 votes

When a particle is created or destroyed, energy is conserved. Energy is also a property of an electron, but we are not inclined to ask - why is energy conserved when the particle is not, because we ...

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Must velocity be constant velocity?
4 votes

Yes, the velocity can vary. This is the power of the principle. In Newtonian mechanics the idea is that if there is a cloud of particles all with forces between them and so all accelerating, ...

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Suppose we do this experiment in a vacuum, will the small pieces of paper behind the bottle be blown?
4 votes

Using the kinetic theory. The reason there is motion behind the bottle is that the particles of gas bounce off other particles of gas to move those behind the bottle. If there is only one particle of ...

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How do we know that experimental evidence of special relativity can't be attributed to other, unrelated effects?
2 votes

The primary justification for special relativity is not that muons last longer as they fall through the atomosphere at high speed. That is just an implication to check the otherwise well confirmed ...

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Would a world-sheet through phase-space make sense?
2 votes

Regardless of whether it is in configuration space or phase space, the 1-dimensionality of the world line is because time is 1-dimensional. As a path, the world line is essentially parameterised by ...

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Why does the air at the top of the wing move down?
2 votes

Lift is generated by conservation of momentum. The wing causes air to be directed more downward, to gain momentum downward, and that is balanced by the upward momentum of the aircraft. It is a ...

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What does color represent in quarks?
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2 votes

It is not electromagnetism, but it is a charge. For example, while there is an electric charge and this gives the strength of the effect of an electric field on a particle, there is also gravitational ...

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Significance of sliding switch in a LR circuit
1 votes

For an inductor, the rate of change of the current is proportional to the voltage. That is, if you try to stop the current in the inductor suddenly, as you do if you simply open circuit it, it will ...

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What causes an atom to move to a vacuum?
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1 votes

In the simplest case, consider an open jar of air. The atoms move around randomly, and in fact exchange with atoms from the air around. When the jar is put in the vacuum the atoms that leave are not ...

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In neutrino absorption, what is it really that absorbs the neutrino?
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1 votes

It could be said that in proton + neutrino = neutron + electron, an up quark in the proton is converted to a down quark in the neutron, using up 2.2 Mev. But also leaving us short on 1 electron charge....

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How quantum field explains magnetic forces?
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1 votes

Quantum mechanics does not deal with forces so much as energy and momentum. Force is the rate of change of momentum with time or energy with position. If a couple of electrons, thought of for now as ...

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What happens when a weapon breaks on impact?
1 votes

My take on this is that the answer involves clarifying the question. You do not transfer force you apply it. You transfer momentum - force times time. The amount that you push back your opponent is ...

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If there is no absolute time, how can we say the Big Bang was 13.8 billion years ago?
1 votes

In the right frame, all the galaxies are approximately stationary. That is - the relative velocity of the galaxies is mostly due to the expansion of space. So, the age of the universe can be computed ...

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Characteristics of pressure in liquid
1 votes

The hydrostatic pressure is the weight of the volume of liquid that the blob of liquid is holding up. That is - the weight of the liquid directly above the blob. The liquid a bit to the side is held ...

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FIeld configuration with just one particle
1 votes

If I got that right - the core of the question is really - why complex numbers. I am also not fond of canonical quantization, in particular because any complex field is representable as two real ...

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Is cosmological constant some kind of field that permeates all of space?
0 votes

The cosmological constant has the same effect as an intrinsic energy density. Although it was introduced as a constant, and intended to be positive, you can build the theory with a negative ...

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What is the definition of a 'branch' in the many-worlds interpretation (MWI) of quantum mechanics?
0 votes

It is not the only way to define it, but I think that the neatest way is as follows. Consider all the possible universes from start to finish. The state of the observed universe is a complex linear ...

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Special relativity and tensile stress
0 votes

The moving observer won't see any stress. This is essentially Bell's spaceship paradox. http://math.ucr.edu/home/baez/physics/Relativity/SR/BellSpaceships/spaceship_puzzle.html From the point of ...

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Is "Air-gen" really possible, and how is it different from perpetual motion?
0 votes

I only read a couple of web articles, after you asked the question. But, it seems to me that the researchers give no explanation for the phenomenon and their conclusion that it is extracting energy ...

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The force on loose end of a membrane
0 votes

If you stretch a stretchy square rubber sheet out so that the left and right edges are kept straight and parallel, but the top and bottom are otherwise unconstrained, then the top and botton edges ...

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Double slit for electrons (two beams or one)?
0 votes

In the Copenhagen interpretation, the principle is that there is a wave and that wave difracts through the holes like any other wave. The electron as a particle then appears at the screen with a ...

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Help using the definition of Hermitian operator in $\int\psi^*(\hat F-\left<F\right>)^2\psi dr$
0 votes

It is usually assumed that $\psi$ can be expressed as a linear sum $\sum_i a_i\psi_i$ of eigen function $\psi_i$ with eigen values $\lambda_i$. So $F \psi = \sum_i a_i\lambda_i\psi_i$. This converts ...

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Isn't the standard proof of a classical electron's orbit invalid?
0 votes

In the core orthodox literature it is taken granted that the instability of the classical electron orbit has been established - essentially because of the principle that an accelerating charge ...

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