# Questions tagged [geometry]

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

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### How do I find the longitude of the subsolar point? [duplicate]

On December 21, 2018 at 2:23pm PST I want to be standing as directly under the sun as humanly possible. Obviously the latitude of that point will be the Tropic of Capricorn. Assuming I have the right ...
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### Optics(interference) [closed]

I'm a student at physics department, and I have a question about optics. In interference phenomenon we have two experiments: one with name Michelson and the other is the double slit experiment. In ...
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### Why can an object not be pulled beyond the polygon which is forming from the attachment points?

I am looking for the physical equations that explains why a 2D object on a 2D surface, e.g. a rectangle cannot be pulled further than the greatest/smallest x/y coordinates of the points it is attached ...
56 views

### Is a displacement a vector, a line segment, or something else?

It probably seems ridiculously naive of me to ask such a basic question, but I have a need to use accurate language. Typically, I think of a displacement as a directed line segment whose end-points ...
219 views

### How does projective geometry related with Fourier transform via Lorentz transformation?

On one hand, the Lorentz transformation plays an important role in classical electromagnetism. On the other hand, each Lorentz tranformation is also a Möbius transformation of $\Bbb C$ (Needham, ...
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### Moment of Inertia of an Equilateral Triangular Plate [closed]

I was reading about moment of inertia on Wikipedia and thought it was weird that it had common values for shapes like tetrehedron and cuboids but not triangular prisms or triangular plates, so I tried ...
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### The commutation of partial derivatives in curved spacetime

While following a lecture series on General Relativity, an argument was presented that in order the spacetime to be flat, a vector parallel transported along two different paths should yield the same ...
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### The shortest distance along the surface of the sphere [closed]

Imagine we have a sphere. And inside the sphere there are two points. Now we have an arc that is connecting these two points and it is said that arc that goes through the center of the sphere is the ...
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### Geometry of gauge theory [duplicate]

In this Ted talk The Geometry of Particle Physics: Garrett Lisi at TEDxMaui 2013 is he referring to the gauge group space while using the toys ? (Seems so to me). Can someone provide some references ...
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### Why does the Earth not cast a shadow straight like a cylinder in the opposite direction of the Sun?

Why does the Earth's not cast a shadow straight like a cylinder in the opposite direction of the sun? Instead, it forms "cones," the umbra and penumbra.
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### Algorithmic approach to finding two vectors that span a plane

I am working on an experiment where I need to align a magnetic field to be parallel to a nanoscale wire embedden in a microscale planar structure. My tools for doing so are two-fold: the planar ...
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### Angle in a triangle [closed]

The question I'm dealing with here deals with mechanics but my specific question concerns the geometry of the shapes involved (I didn't post this to the math stack exchange because it's more likely ...
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### Minimum force needed to start a wheel on a slope?

I have been messing up with this for at least two hours , but can seem to find anything rather than a small angle! The question is to find the magnitude and the direction of the smallest force (say ...
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### Proving the centre of mass formula with integral [closed]

I came across a question: Find $f(r)$ and prove the centre of mass formula: $$\vec{r_{cm}} = \frac{1}{V} \int f(r) \vec{dS}$$ Where $V$ is the total volume and our surface integral is ...
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### Collision detection of two circles rotating around fixed points in 2D [closed]

Recently I have learned how to predict the time of collision between two circles moving linearly. Positions of $P$ and $Q$ after time $t$ are: $P(t) = P_0 + vPt$ $Q(t) = Q_0 + vQt$ The goal was to ...
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### Converting 180° of motion to 270° of motion via gear ratio [closed]

I am very new to math / physics not sure if this is the best network to ask or if math is better but I am working on a project where I only need 270° of motion to turn a potentiometer from a servo ...
656 views

### Rotation in Higher Dimensions

In a world of three spatial dimensions plus time, every atom rotates around a line, the axis of rotation. In a world of $N$ spatial dimensions where $N$ is greater than 3, must every atom rotate, ...
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### Is there a book about projective geometry in physics?

From Complex projective space: In quantum physics, the wave function associated to a pure state of a quantum mechanical system is a probability amplitude, meaning that it has unit norm, and has an ...
As I understand a conformal transformation transforms the metric $g_{mn}\rightarrow f^2(x)g_{mn}$ for some function $f$ that is non-zero everywhere. Why does this preserve angles? I know that $\... 1answer 137 views ### Do we$\textit{need}$to use a torsion-less connection(Riemann-Levi Civita) in General Relativity? While learning General Relativity, we always use the Levi-Civita connection, which has the special property of being torsion-less. My question is: Do we need to use a torsion-less connection to study ... 1answer 202 views ### What does the Kretschmann scalar really tell us about the geometry of spacetime? [duplicate] The Kretschmann scalar is one of the measures of spacetime curvature. For flat (Minkowski) spacetime it is zero. The dimensions of the Kretschmann scalar are$[L]^{-4}$. What does that physically ... 3answers 821 views ### Painting with a Pendulum: Would it be possible to graph the pattern? I intend to try and replicate an experiment that I found online: The idea seems to be: Attach a string to a fixed, overhead object Attach a can of paint to the string Put a hole in the bottom of the ... 1answer 46 views ### In order for spherical mirror to focus, why do we need$\mu > h_1\$?
We know that in order for a spherical mirror to focus, the equation $$y^2 = 4fx - x^2$$ do behave like the parabola equation $$y^2 = 4fx,$$ so we need $$f>> x.$$ However, it is told me that the ...