Questions tagged [point-particles]
The point-particles tag has no usage guidance.
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How do I compute the stress-energy tensor for a simple system of $N$ point particles?
I haven't been able to find a simple self-contained definition of the stress-energy tensor as used in the Einstein field equations.
Suppose I have $N$ classical (not quantum) point particles with ...
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Average distance travelled by particle points placed uniformly at random in a sphere with speed $||v||$ and direction uniformly random?
I would like to compute the average distance travelled by particle points at constant speed $v>0$ with uniformly-distributed directions and placed uniformly at random inside a hollow sphere of ...
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Quantization of charge implying charge exist in the form of point particles
The statement for quantization of charge says that total charge of a body is constant. Now the word " body " seems vague. We may consider any part of space which we want and call it a body. ...
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Can a point charge be asymmetric?
The derivation of Coulombs law from Maxwell's first equation for a point charge assumes that the field is symmetric along a sphere. What happens if this assumption is removed? Could there be other ...
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Lagrangian for a free antimatter particle
Context
The Lagrangian, $L$, of a free particle is derived many places including in Section 8 of Landau's Theory of Classical Fields. The well-known result for a free material particle of mass $m$ and ...
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What do we learn from quantizing the relativistic point particle?
In many textbooks on string theory, some time is spend on quantizing the relativistic point particle as a warming-up for quantizing the Nambu-Goto action for relativistic strings.
However, I have not ...
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Is there a Lorentz invariant action for a free multi-particle system?
I want to write down a Lorentz-invariant action of free multi-particle systems.
I know that a Lorentz-invariant action for each particle might be expressed as
$$
S[\vec{r}]=\int dt L(\vec{r}(t),\dot{\...
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Finding the equipotential surface of a system of two unequal oppositely charged point charges [closed]
We have a system of two unequal opposite point charges, of which $q_2$ is smaller and $d$ is the distance between charges. There is an equipotential spherical surface of potential $V=0$ that encloses ...
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Does classical electrodynamics have a Lagrangian that gives both the Lorentz force and Maxwell equations?
There is a Lagrangian for a particle of mass $m$ and charge $q$
$$\mathcal{L}_1 = \mathcal{L}_k(m, \vec{v}) - q\phi + q\vec{v}\cdot\vec{A}$$
where $\mathcal{L}_k(m, \vec{v})$ is either $\frac{1}{2}m\...
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Derivation by Zee of a relativistic point particle action in a EM field in curved space
In Einstein Gravity in a Nutshell by Zee, in section IV.1 page 241, he tries to write down the action for electromagnetism and gravity in an intuitive and patchwork way,
Starting from the relativistic ...
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Constraints Generating Gauge Transformations and BRST
Given a gauge-invariant point particle action with first class primary constraints $\phi_a$ of the form ([1], eq. (2.36))
$$S = \int d \tau[p_I \dot{q}^I - u^a \phi_a]\tag{1}$$
we know immediately, ...
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Continuity equation in curved space-time: a point particle
Let us consider the action describing a point particle with charge $e$. The interaction term is equal to
$$
S_{int} = e\int A_{\mu}\dfrac{d{x}_e^{\mu}}{d\tau}d\tau = e\int A_{\mu}\dot{x}_e^{\mu}dt
$$
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How to determine whether an object is a point object?
I know that we can consider an object as point object, if its size is negligible as compared to distance traveled by it in reasonable amount of time. But in my book Ncert there is questions which asks ...
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2D newtonian gravitational flux not the same for centered/offset point mass? [closed]
$\alpha*r$" />
I am having trouble comparing the 2-dimensional gravitational flux, due to a point mass $M$ located at the origin of the gaussian circle (in green) at point O, versus a point mass ...
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How does normal force act on ring with a point mass on it? [closed]
I have been thinking about this situation, I have no idea how the normal force act of such a body.
Here I have taken the point mass and ring of same mass m but please provide a general solution.
So I ...
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