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Questions tagged [mathematical-physics]

DO NOT USE THIS TAG for elementary physical questions. This tag is intended for questions on modern mathematical methods used in quantum theory, general relativity, string theory, integrable system etc at an advanced undergraduate or graduate level.

"Mathematical physics consists of the application of mathematics to problems in physics and the development of mathematical methods suitable for such applications and for the formulation of physical theories." (from Journal of Mathematical Physics). This tag is intended for questions on mathematical methods used in quantum theory, general relativity, string theory, integrable system etc at an advanced undergraduate or graduate level.

Do not use just because your question involves physics!

See also Physics Stack Exchange's discussion on mathematical physics, Math Overflow's discussion on mathematical physics and Physics Overflow for further reference.

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What is meant by "collective behavior" in the definition of plasma?

"Plasmas are many-body systems, with enough mobile charged particles to cause some collective behavior ." [M.S. Murillo and J.C.Weisheit Physics Reports 302, 1-65 (1998)]. In the above definition what is meant by "collective behavior" ?
nmasanta
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find a formula to cacluate if a moving object goes to a target

I am struggling to find a formula to calculate if a moving object goes towards a certain direction. I have $P_1$, which is the current position $(x_1, y_1)$, and its direction angle. I also have the position of a target $(x_2, y_2)$. How can I…
Aody
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How to prove a relation between the evolution operators in the Schrödinger and interaction pictures of quantum mechanics?

Consider a Hamiltonian $H$ of two components, a time-independent $H_0$ and a time-dependent $V(t)$, $$H(t)=H_0+V(t)\,.$$ In the Schrödinger picture of quantum mechanics, the state $\left|\psi(t)\right\rangle_{\mathrm{S}}$ evolves according…
Ambrose Chau
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Is there a proof that a function which satisfies these axioms of relativity must be linear?

Let us only consider the 2 dimensional case where the two frames of reference coincide at the origin. For each $v\in (-c,c)$, let $f_v:\mathbb{R}^2\to\mathbb{R}^2$ be a smooth function satisfying the following conditions (with the first coordinate…
John B
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How to derive Torque formular $\tau = \omega\times I \omega + I\dot{\omega}$

Here is the formula I am trying to derive: $$\tau = \omega\times I \omega + I\dot{\omega}$$ where $\tau$ is the torque. $\dot{\omega}$ is the angular acceleration. $I$ is the moment of inertia. $\omega$ is the angular velocity. This is what I tried.…
Di Wang
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From where does this - ve sign come from

Let θ=54 5θ=270 2θ+3θ=270 2θ=270-3θ sin(2θ)=sin(270-3θ) sin(2θ)= -cos(3θ) From where does -ve sign come from? 270-3θ will be in 2quad where sin is +ve.
Fareed
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how to plug height and time into a quadratic equation $h=at^2+bt+c$

How to plug height and time into a quadratic equation $$h=at^2+bt+c$$ to model the height of the object $t$ seconds after it is shot into the air? The height is $163.6$ feet the time is $1.2$ seconds. Is it like this: $$h=163.6(1.2)^2+163.3(1.2)+0$$
student
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Principle of transmissibility of forces

My textbook states this principle as follows " The conditions of equilibrium or of motion of a rigid body will remain unchanged if a force acting at a given point of the rigid body is replaced by a force of the same magnitude and same direction, but…
Sai Teja
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Hookes law Bungee jumping question

ive seen a few forums with answers for these but im finding a fair few different results and im getting confused. Perhaps someone here can help: A bungee rope is specially designed and its modulus of elasticity is such that the rope is stretched to…
EthanOliver
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calculating age of rock sample

I have the question: "If a rock has a parent:daughter isotope ratio of 1:10 and the parent isotope is Rb-87, given that the half-life of Rb-87 is 48800 x 10^6 years. Calculate the age of the rock sample. " here is my attempt is this correct ? Parent…
Dan
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Compute time required to travel given distance with constant acceleration and known initial speed

What informations I have: Distance to travel Initial speed Acceleration (constant) What I need: Time it will take to travel that distance in the given conditions. What would be the formula that gives me that? If this answer is correct, the…
cyphics
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Calculating temperature of gas

I have the question "A container had 6 moles of an ideal gas. In an experiment, the pressure of the gas and its volume were measured at constant temperature. The following readings were obtained and plotted on the graph on the next page Determine…
Dan
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How fast must the ball be launched to land 450 feet away?

A golf ball is hit in a horizontal direction off the top edge of a building that is $100$ feet tall. How fast must the ball be launched to land 450 feet away? I have some of the equations that I have been working with…
Alana
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Finding the energy levels of an electron in a plane perpendicular to a uniform magnetic field

Suppose we have an electron, mass $m$, charge $-e$, moving in a plane perpendicular to a uniform magnetic field $\vec{B}=(0,0,B)$. Let $\vec{x}=(x_1,x_2,0)$ be its position and $P_i,X_i$ be the position and momentum operators. The electron has…
Freeman
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About a type of equations

In physics, there appear a type of equations following this format, $ Q2 = Q1(1 + a \Delta T) $ Where Q1 is the first quantity Q2 is the changed quantity, a is the changing coefficient, $ \Delta T $ is the change of the factor (for example,…
practronix512
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