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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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, ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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....

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...