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Results tagged with reference-frames
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user 36793
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.
11
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answers
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Understanding the CMB background as a reference frame
We say the Earth is in relative motion with respect to the cosmic microwave background (CMB), causing anisotropies in the CMB spectrum. I have four very simple questions about this.
How is it possib …
- 27.2k
4
votes
1
answer
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How does one find the wavefunction of a particle in its rest frame?
In classical mechanics, the orbital angular momentum of a particle is defined as $\textbf{L}=\textbf{r}\times\textbf{p}$. This is zero in the rest frame of the particle where $\textbf{p}=0$.
Quantum …
- 27.2k
4
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answer
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Noether's theorem and Invariance of Lagrangian under translation
Consider a coordinate system in which the point A has coordinate $z_0$ and point B has ccordinate $z$ where there is a particle of mass $m$. Let there be a constant gravitational field of Earth. The L …
- 27.2k
2
votes
2
answers
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Meaning of general coordinate invariance: distinguishing inertial and non-inertial observers
Laws of physics cannot distinguish one inertial frame from another which is equivalent to the statement of Poincaré invariance.
What is the meaning of general coordinate invariance? General coordina …
- 27.2k
2
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Accepted
Why is the centripetal net force always to the center?
$\bullet$ Note that the direction of the change in the velocity $\Delta\textbf{v}$ is towards the center. Therefore, the acceleration must be towards the center and hence also the force. Your diagram …
- 27.2k
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Why the clock at rest runs faster, while another clock slows when moving?
The situation is completely symmetric. Let the velocity of a frame A w.r.t another frame B is $\textbf{v}$. then from the perspective of A, the frame frame B has a relative velocity $-\textbf{v}$. Fro …
- 27.2k
1
vote
1
answer
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Which time is there in the FRW metric?
The FRW metric is given by $$ds^2=dt^2-a^2(t)\Big[\frac{dr^2}{1-kr^2}+r^2(d\theta)^2+(r\sin\theta)^2(d\phi)^2\Big].$$ There is a time $t$ sitting in this metric. In which frame is this time measured?
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