Questions tagged [point-particles]

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23 questions with no upvoted or accepted answers
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Do charges have spatial dimension?

I don't know much about anything in physics. I hope you can bear with that. Let me start with my question do charges have any dimension, by this I mean physical dimension like length, breadth, height ...
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0answers
47 views

Actions for relativistic point-particles of higher spin

To describe the behavior of a relativistic point-particle, we have the standard action $$S=\int d\tau \bigg[\frac{1}{e} \dot X^\mu\dot X_\mu +m^2 e\bigg], $$ where $e$ is the worldline einbein. Then, ...
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0answers
37 views

Is there a code for Ewald Summation for Dipoles?

Does anybody know if there exists a code that calculates the potential energy for a system with both point charges and point dipoles using Ewald summation? This would be a great help to my Master ...
2
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1answer
180 views

Deriving the 4-momentum of a free particle moving in curved spacetime

Consider a free particle with rest mass $m$ moving along a geodesic in some curved spacetime with metric $g_{\mu\nu}$: $$S=-m\int d\tau=-m\int\Big(\frac{d\tau}{d\lambda}\Big)d\lambda=\int L\ d\lambda\...
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0answers
62 views

Motion of a catapulted point mass moving freely inside a spherical bucket

I am trying to study the motion of a point mass inside the bucket of a catapult. The catapult is shooting downward (i.e. describing a rotation of 180° from the horizontal axis) and I would like to ...
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0answers
300 views

Idealizations of an object as a point particle

Why is it that an object can be idealized as a point particle or 'particle like' to solve problems? What are the limits of such a tool?
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0answers
59 views

Charged particle interacting with electromagnetism and gravity

Consider a classically charged point particle interacting with electromagnetism and gravity. The relevant dynamical variables are $\chi^\mu (\tau)$ of the particle, the electromangetic potential $A_\...
1
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1answer
194 views

Relationship between stress-energy tensor for a point particle and its Lagrangian

The Lagrangian for a (relativistic) point particle with rest mass $m$ and velocity $v$ is: $$L=-\frac{m}{\gamma (v)}$$ (using $c=1$). Over on Wikipedia we can find the Stress-energy tensor for said ...
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0answers
30 views

Extended SUSY and superspace

I am trying to understand how to construct an action using the superspace formalism for $\mathcal N>1$. I have read that this is quite difficult to do, so let's consider a simple example. Suppose I ...
1
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1answer
51 views

Electromagnetic field of a point charge seen from a rotating reference frame

Let us consider a point charge sitting in the origin of our coordinate system. If we change to a rotating system, will the field of the point charge still look the same? Intuitively I would say yes, ...
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0answers
24 views

Equilibration of a solid body with two points particles

How do I find $\theta$ as it $\theta (m,d,l) and AB=L$? And the cane which holds the two points particles(mass) is massless . In A the point mass is $3M$ and in B the mass is $M$ where there is no ...
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0answers
96 views

Integrating Out Auxiliary Field of point-particle Polyakov Action

The Polyakov action of a point-particle is $$S[X,e]=\frac{1}{2}\int d\tau\left(\frac{\dot{X}^{2}}{e}-m^{2}e\right)$$ with the $(−,+,+,+)$ Minkowski sign convention. How to perform the path-integral ...
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1answer
136 views

What is the induced electromagnetic field of a point charge?

If I move a point charge on some trajectory, then it will produce an electric field as well as a magnetic field. As the charge is moving, and as a point charge can not produce a steady current, then ...
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1answer
308 views

Energy density of a 0D point particle vs. a 1D string

As I understand there is a problem in physics where point-like massive (or charged, etc.) particles would have infinite mass/energy (or charge, etc.) density. I'm curious how in the context of String ...
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1answer
187 views

Do elementary particles have a density?

The SM supposes elementary particles are structureless unless composite objects like hadrons. For bosons, that can occupy the same state, we can define energy or mass density. The same happens but ...
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2answers
71 views

Does the propagation of light through spacetime, with regards to how we describe it, depend on when a photon is a wave function or point particle?

When for example, a photon is emitted from an atom, does that photon propagate through spacetime in all directions away from the atom in the form of a sphere (Wave Function) and then at some point ...
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1answer
42 views

Is this a sufficient condition for a stable equilibrium point?

My question is based on thinking about a point particle in electromagnetic fields, but the idea should apply to other problems. The point $\mathbf x_0$ is an equilibrium point of the force field $\...
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0answers
38 views

Point particle and angular deficit

I would like to understand in what sense an angular deficit can be interpreted as a point particle. Typically, if you have a metric in polar coordinates such as: $$ds^2 = -dt^2 + a^2(t,r) dr^2 + r^2 d\...
0
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1answer
51 views

Why the continuous arrangement of point masses (particles) at infinitesimal separations leads to a extended system?

I am basically talking in terms of Newtonian mechanics. The Newton's laws started with a good and easy assumption of particles as point masses. This assumption clearly reformed physics and a great ...
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1answer
59 views

Question about point particle vs. wave equation location

Another uncertainty question, this came up in another forum. As I understand it an electron, for example, is a point-like particle. I take this to mean it exhibits dimensionless properties, but ...
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0answers
110 views

Energy of single particle is equal to energy of multiparticle system it consists of?

The solution to a problem of atom fission led me to this question. In this problem the mass of original atom nucleus, masses of two child atom nuclei as well as zero kinetic energy of first atom ...
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1answer
35 views

Real points vs. Physical points and what replaces them

Quantum field theory and relativity share the need for point particles (besides we have learned how to deal with extended objects with more or less success). Heisenberg uncertainty principle ...
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1answer
57 views

point particle explanation of refraction

Is there an explanation of refraction using the point particle model? Most explanations I have seen use the wave model or particles with width.