# Tagged Questions

A set of numbers used to quantify location in space.

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### Shear stress in cylindrical coordinates?

In cylindrical coordinates the momentum flux is given by (in the $r$ direction): $$\Pi=-\eta \frac{\partial (r\omega)}{\partial r}$$ Where $\eta$ is the viscosity. Therefore one would expect that the ...
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### How can I convert Right Ascension and declination to distances?

I am calculating galaxy rotation curves for various galaxies in Ursa Major cluster and I want distance of those galaxies from the centre of Cluster. The values referred as coordinated are RA and dec ...
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### For a giving metric in GR, how do we learn which observer the metric refer to?

For example, I have been told the Schwarzschild observer is far away from blackhole and events,(namely, I think, the observer is static at infinity of the coordinate.) And the second example,the ...
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### Conversion of satellite coordinates from ITRF to J2000

I have coordinates of various satellites in two coordinate systems: Cartesian coordinates in the international terrestrial reference frame (ITRF) RA / DEC in J2000 epoch, as derived from plate ...
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### Clarification in deriving the radial momentum operator $p_r$

In deriving an expression for $p_r$, a particle's radial momentum, I am unsure what is happening at a certain step. The derivation given in The Physics of Quantum Mechanics by Binney and Skinner is as ...
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### Change of coordinates [duplicate]

this year I finished off my course of Physics I (the first general physics) at my university and we had a lot of exercises to do where in order to complete them I had to change the system coordinates, ...
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### Operational Definition of Reference Frame in General Relativity

Most treatments of GR begin with the assumption that spacetime is a pseudo-Riemannian manifold (or, sometimes, that it is a more general manifold). But this entails quite a few tacit assumptions about ...
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### Velocity and acceleration (as vectors) in a straight line

A student is trying to determine the acceleration of a feather as she drops it to the ground. If the student is looking to achieve a positive velocity and positive acceleration, what is the most ...
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### Why the $g_{00}$ of the Robetson-Walker metric is 1? [closed]

Why it not depends on another variable?
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### Describing the shape of a singularity

Hawking and Ellis write about the difficulty of describing the shape of a singularity when presented with a manifold that has curves of finite length that don't reach a point in the manifold. [...
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### Is Gauss electric flux law valid in all coordinate systems?

The derivation of Gauss electric flux is as follows : $$\iint{\vec{E}}\cdot{\vec{dS}}=\iint E \, dS \cos\theta \, .$$ The projection of infinitesimal area on the surface $\vec{dS}$ on the radial ...
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### What is considered now over astronomical distances?

For the sake of discussion, let's say that Mars is exactly 5 light-minutes away and that Earth and Mars are moving with the exact same velocity so that special relativistic effects are irrelevant. Let'...
In A. Zee's Einstein Gravity in a Nutshell, he starts with the following expansion of the metric at some point $P$ of a Riemannian manifold, with coordinates $x^\mu$ that have the origin at $P$: $$... 1answer 31 views ### The equation of continuity in isothermal system in spherical axis(transport phenomena) My homework is about finding the equation of continuity in isothermal systems in spherical axis, I can't imagine a workaround for that since its a little complicated for me to understand velocities ... 0answers 257 views ### Confusion between primed and unprimed coordinates While deriving Ampere's law in Magnetostatics we come across a term \nabla\times J(r') = 0 and the reasoning we give is because current density is only a function of primed coordinates hence it's ... 1answer 119 views ### Trajectory of a projectile in a three dimensional space [closed] g: the gravitational acceleration—usually taken to be 9.81\:\mathrm{m/s^2} near the Earth's surface θ: the angle at which the projectile is launched v: the speed at which the projectile is ... 1answer 64 views ### \frac{d}{dr}=0 and \frac{d}{dz}=0 (cylindrical coordinates) for a 1D ring In http://ritchie.chem.ox.ac.uk/Grant%20Teaching/2010/Lecture%204%202010.pdf slide 21 of 26, he says "Radius of ring is fixed and so derivatives in r are 0." Presumably this goes for \frac{d}{... 1answer 57 views ### In central-force mechanics, how do we substitute ξ=\frac{1}{r}? I have taken a look at central-force mechanics in the past, but I still cannot understand how ξ=\frac{1}{r} is substituted to find \frac{d^2r}{dt^2} in terms of ξ. So I know from F=ma that:$$(...
Ws can re-arrange the standard Schwarzschild metric as $$\left(\frac{d\tau}{dt}\right)^2=\frac{r-1}{r}\left[1-\left(\frac{r}{r-1}\frac{dr}{dt}\right)^2\right]$$ Where $\frac{r-1}{r}$ is the local ...