重度肠化是什么意思
百度 因此，买一辆纯电动汽车，“充电”是否方便是困扰消费者的最直接因素。
A reference frame is a particular coordinate system chosen to represent physical entities. The notion is most often used in special and general relativity to denote particular coordinates chosen on the spacetime manifold.
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Why does the bar in the gym not fall when one side is loaded with weight?
Lately I observed that the bars that is used to do bench press in gym don't immediately fall on the side loaded with weight. Which does not sound correct intuitively, the bar should fall down because ...
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In what situations may we use the center of mass for calculations?
On the Wikipedia chapter on the center of gravity, there is a calculation that shows that the center of mass is a point about which a uniform, unidirectional gravitational force does not cause torque.
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Does magnetic field vary when frame of reference changes?
This question comes from a photo of my homework. There is a light stick with two balls on both side. I've balanced the weight of them so they could rotate freely around the point O. The ball on the ...
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Interpretation of the lorentz-invarient transition rates (LI Fermi's Golden Rule)
As I'm studying for my particle physics exam I have noticed that I do not know how to interpret the lorentz-invariant Fermi's Golden Rule. Or more precisely the transition rate $\Gamma_{fi}$.
For ...
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Is Newton's first law based on inertia or frame of reference? [duplicate]
Our Physics Sir in class said that the first law isn't law of inertia..
I asked for clarification but he only said its based on frame of reference. Till now, we were always taught that Newton's First ...
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Advantage of launching a rocket from the Equator
I have recently read the following in a book:
As a result of the Earth’s rotation, objects on its surface would be
flung off were it not for the Earth’s gravity holding them down. In
fact, this “...
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Does fixing a $z$-axis and state also fix other coordinate axes in quantum mechanics?
Say we have an EPR pair $|\psi\rangle := (|00\rangle + |11\rangle)/\sqrt{2}$, where $|0\rangle, |1\rangle$ denote the Z-axis eigenstates of, say, a spin-1/2 particle. We measure both parts of the ...
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Can a photon be gravitationally redshifted if it has no mass?
Gravity affects all energy, including photons, but what’s actually happening to a massless particle as it climbs out of a gravity well? Does its wavelength “stretch” in transit, or does spacetime ...
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Are center of rotation and center of mass are same for an ellipsoid falling in water under gravity?
Consider an ellipsoid solid freely falling under gravity in water. The solid is free to rotate and translate inside water. If gravity is the only force acting, I understand that center of mass and ...
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Relationship Between Inertial Frames and Forces
I have some questions that have been bothering me for a while, about the relationship between the definition of an inertial frame, and the way in which we identify forces.
Newton's First Law says, ...
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Is angular momentum balanced locally?
So consider the balance of angular momentum for a system of particles
$$ \sum r_i \times F_{iext} = \frac{dL}{dt} \tag{1} $$
If no external forces are present, RHS vanishes, and thus, that implies ...
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Can entropy decrease for an observer in a different frame of reference?
Thermodynamics says entropy must increase, but is this observer-dependent like simultaneity? Could entropy flow or second law interpretations vary across reference frames in relativistic scenarios?
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Doubt regarding method to find centre of mass of a cone
I was trying a certain method to find the centre of mass of the cone i.e. to prove that for a solid cone, the centre of mass is 1/4th the height from the base . This method involves cutting the cone ...
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Can a uniformly accelerating charge radiate in all reference frames?
In an inertial frame, an accelerating charge emits radiation. But what happens in a co-accelerating frame? Does radiation still exist, or is it frame-dependent? And what does this imply about energy ...
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Why do fictitious forces in a rotating frame produce real accelerations even though they don’t obey Newton’s 3rd law?
I’ve been working closely on understanding some features of reference frames and have come across a fundamental derivation of the so?called “fictitious” forces acting within a rotating reference frame....
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