Questions tagged [faq]
Frequently asked questions. Whenever the same question winds up getting asked over and over again, this tag should designate the _original_ one, which we close all the others as duplicates of.
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Why does it represent change in velocity?
In the above image a particle goes with velocity $v_0$ at some direction and then in an another direction where its velocity is represented by $v$. Both are same in magnitude but their direction is ...
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Is energy only the change in spacetime of an object with respect to an observer?
It is fact that there is only kinetic energy that is eligible to do some work. Even the, EM energies are the kinetic energy of quantum particles such as photons. Kinetic energy for an well defined ...
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Is it possible to speak about changes in a physical constant which is not dimensionless?
Every so often, one sees on this site* or in the news† or in journal articles‡ a statement of the form "we have measured a change in such-and-such fundamental constant" (or, perhaps more commonly, "we ...
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Given Newton's third law, why are things capable of moving?
Given Newton's third law, why is there motion at all? Should not all forces even themselves out, so nothing moves at all?
When I push a table using my finger, the table applies the same force onto my ...
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How do Einstein's field equations come out of string theory?
The classical theory of spacetime geometry that we call gravity is described at its core by the Einstein field equations, which relate the curvature of spacetime to the distribution of matter and ...
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What was Albert Einstein's proof for $E=mc^2$?
Most people know the famous equation:
$$E=mc^2$$
What were his steps of thinking for this equation that helped us discover so much about our world?
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How does the Higgs Boson gain mass itself?
If the Higgs field gives mass to particles, and the Higgs boson itself has mass, does this mean there is some kind of self-interaction?
Also, does the Higgs Boson have zero rest mass and so move at ...
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How does gravity work underground?
Would the effect of gravity on me change if I were to dig a very deep hole and stand in it? If so, how would it change? Am I more likely to be pulled downwards, or pulled towards the edges of the hole?...
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Is it possible to recover Classical Mechanics from Schrödinger's equation?
Let me explain in details. Let $\Psi=\Psi(x,t)$ be the wave function of a particle moving in a unidimensional space. Is there a way of writing $\Psi(x,t)$ so that $|\Psi(x,t)|^2$ represents the ...
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Dependence of Friction on Area
Is friction really independent of area? The friction force, $f_s = \mu_s N$. The equation says that friction only depends on the normal force, which is $ N = W = mg$, and nature of sliding surface, ...
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Resource recommendations [closed]
Every once in a while, we get a question asking for a book or other educational reference on a particular topic at a particular level. This is a meta-question that collects all those links together. ...
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Can energy be taken out of the QFT vacuum?
There have been recent questions about the vacuum. In my simplified knowledge the vacuum is like a ground state energy level, and also that there might even exist other lower energy levels than the ...
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What is the simplest way to prove the Earth is round?
Assume you've come in contact with a tribe of people cut off from the rest of the world, or you've gone back in time several thousand years, or (more likely) you've got a numbskull cousin.
How would ...
tQuarella
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Why can't light escape from a classical black hole?
Photons do not have (rest) mass (that's why they can move at the speed of "light").
So my question is: how can the gravity of a classical$^1$ black hole stop light from escaping?
--
$^1$ We ...
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Why there's a whirl when you drain the bathtub?
At first I thought it's because of Coriolis, but then someone told me that at the bathtub scale that's not the predominant force in this phenomenon.
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