# Questions tagged [geometry]

To be used for questions on geometry closely pertaining to physics. Includes differential geometry and euclidean geometry.

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### Center of mass of hemisphere

While calculating the center of mass for hemisphere, In solid hemisphere, we can calculate without taking the trignometric limit, Elements can be taken in terms of $y$ (vertical axis) and I got the ...
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### For the vector in the $yz$ plane lying halfway between the $y$ and $z$ axes, how to find $\phi$? [closed]

I am solving a problem in spherical coordinates , there we have condition that a vector in the $yz$ plane lying halfway between the $y$ and $z$ axes. For this we take $\theta = \pi/4$ and $\phi= \pi/2$...
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### Sign of components of $\vec{L}$ seems to change under parity; book says otherwise

Book: Gravitational Waves-Vol 1 by Maggiore; pg 147, note 48 The book says that the components of angular momentum $\vec{L}$ are unchanged under parity (reversing the orientation of the axes). Now, ...
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### How to find resultant vector's angle? [closed]

Hi there, I am confused about why the vector diagram in the answers for the question above is drawn as such. I thought it would be drawn like this: My vector diagram gives a resultant vector which ...
44 views

### Finding the distance travelled by a fly in a room from one lower corner to the diagonally opposite one [closed]

A room has a length of 4 meters, width of 5 meters and height of 3 meters. A fly is on one of the corners and walks to the diagonally opposite one. What is the length of the shortest possible ...
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### Why do mirrors reflect light while regular surfaces don't?

i understand about reflection and how we see light but what confuses me is; all objects that can be seen reflect light (besides black obviously) and mirrors also reflect light. so why does one produce ...
43 views

### Would it take more, or less than twice the force to inflate a balloon to a radius twice as big? [duplicate]

I'm making a set of exercises as part of a college project, aimed at 4th year middle school physics. In an exercise on spring constants, i used balloon inflation as a new example, i made the following ...
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### What is the length of the yarn in a ball of yarn? [closed]

The image https://commons.wikimedia.org/wiki/File:Ball_of_yarn_10.jpg shows a typical ball of yarn. Such a spherical ball of radius $R$ has a volume $4πR^3/3$. The radius of the yarn is $r$. How long ...
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### Calculate the changing morphology of a rubber ball

Imagine you have a rubber "bouncy ball" and you push your thumb hard into the ball. Some deformation will occur around your finger. However, the general morphology of the ball won't change in the same ...
31 views

### What is meant by “neighboring points”?

I have recently been frequently encountering the phrase "neighboring points" during my studies. For example: Fermat's Principle. Optical rays travelling between two points, $A$ and $B$, follow a ...
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### If extra dimensions are out there, why don't/can't we see them? [duplicate]

String theory proposes the existence of extra space dimensions. Very brilliant minds believe in their existence. Of course, I could appreciate that they are consequences of mathematical ...
445 views

### Can we see the curvature of a surface?

After reading the Feynman lectures' (chapter 42, Vol.2) , it had me thinking if it is by any way possible to measure the curvature of a surface (think, surface of earth) just by observing the nature ...
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### What's the problem with Euclidean geometry for astronomical phenomena?

This passage from John Pierce, An Introduction to Information Theory: "also note that while Euclidean geometry is a mathematical theory which serves surveyors and navigators admirably in their ...
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### Weird assumption in a paper to prove equation [closed]

Let $M_k$ and $M_{k+1}$ be two successive positions. Supposing the road is perfectly planar and horizontal, as the motion is locally circular, we have: Where $\Delta$ is the length of the circular ...
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### Is every observer equidistant in all directions from the point of origin of the universe? [duplicate]

I am interested in the origin and present structures of the dimensions of space and time. I do not think space/time can be correctly described by an ordered set of scalars: (x,y,z,t). So. If every ...
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### Square gears pitch curve relationships [closed]

I am trying to design square gearset using MATLAB program. I have designed several ones (elliptical, eccentric, spiral, circular ....etc). But when I came to the square gears, I needed the ...
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### Are special conformal transformations continuous?

My understanding of special conformal transformations (SCTs) is fairly limited, but I believe that they are composed of an inversion, a translation and another inversion. Since inversions are discrete ...
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### Why do the rail tracks seem to converge and vanish? [duplicate]

Why do railway tracks seem to converge at a far away point? Can this phenomenon occur with a very far away tall wall (considering I stand on a flat plane, not the curved surface of earth). Isn't ...
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### How did German radio beams reach distant English cities during WWII? [closed]

During WWII, the Germans were using radio beacons (the "Knickebein" system) to guide their bombers into English territory. They set up two beacons, one in Kleve, a city in West Germany, and one at ...
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### How can we find the charge distribution of $n$ external electrons on the surface of a conducting cube? [closed]

Suppose we take 'n' electrons and put them on the surface of a conducting cube. How can we calculate the charge distrubution and position of these electrons once the static situation has been arrived ...
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### General force between two point particles, one of which has “spin”

Consider two points in the empty (isotropic and homogeneous) space: since the only vector that "makes sense" (the only vector that we can define) is the vector given by the difference of the two ...
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### How to determine the minimum force in these questions?

Take a look at this example The author mentioned that the shortest path when the angle is 90 which is clearly obvious. Now take a look at the following problem from the same book The author has ...
### If vector $a$ rotate about vector $b$, does vector $b$ also rotate about vector $a$?
For $2$ vectors $\, \vec a,\vec b$, both originate at $[0,0,0]$: If vector $\vec a$ rotates about vector $\vec b$ when observed from a coordinate system fixed to vector $\vec b$, does vector $\vec b$ ...