Questions tagged [reference-frames]

A reference frame is a particular coordinate system chosen to represent physical entities. The notion is most often used in special and general relativity to denote particular coordinates chosen on the spacetime manifold.

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Suggestions for books on uniform and non-uniform circular motion

With this question I am searching for a universitary or school book where the uniform and non-uniform circular motion is fully treated. I was interested if you could give me some specific details of ...
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Acceleration-Meter

I encountered a Physics Olympiad problem: A ball bearing rests on a ramp fixed to the top of a car which is accelerating horizontally. The position of the ball bearing relative to the ramp is used as ...
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Does electric charge vary between observers?

I understand that certain observations such a length and mass vary depending on observers in different frames of motion and gravity. I was wondering if the electric charge changes in a similar way. ...
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35 views

Vector towards collapsed object [closed]

If an object shrank to point size due to structural collapse under its own mass would the exact center of the object be in the same co-ordinate position as before collapse? For example would a vector ...
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In a general physical sense, is the position of a particle really a vector?

Is it consistent to define the position of a particle in some frame as a vector or is just an informal representation? Velocity and acceleration can be added up and multiplied by real numbers and ...
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Can an ordinary object be a black hole in a different frame of reference? [duplicate]

Suppose by some hand-wavy means, an iron bead of one gram rest mass was moving towards the Sun with kinetic energy equal to the Sun's gravitational binding energy. In the object's frame of reference, ...
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79 views

Surface temperature variation with distance [closed]

So here is the question I'm troubling with: We estimate that the temperature varies approximatively with that relation:
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66 views

Graph analysis of accelerometer data

I used my mobile accelerometer sensor to collect data from a moving bike where I held it in my hand in a way that the smartphone sensor +Y axis is in the direction of the moving bike always. This can ...
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1answer
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Can molecules rotate on any axis?

In statistical physics, the rotation of molecules in a gas can be excited if the temperature is high enough. This rotation is excited in a quantum mechanical way. But is the axis of rotation also ...
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Quantum elevator [closed]

What are the prerequisites for tackling the problem of quantum elevator? Einstein in an elevator is freely falling with another miniature Einstein in his hand ad infinitum. Do all the Einsteins have ...
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Velocity in body frame and inertial frame of the center of mass

Ok so I have this really basic question: I want to reconcile the theorem of relative velocities, which expresses the velocity of a particle, in fact the center of mass of a rigid body, in an inertial ...
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67 views

Components of Angular velocity

Angular velocity vector is defined as, $\overrightarrow{ω} = \widehat{n} \frac{d\theta}{dt}$ where $\widehat{n}$ is an unit vector along the axis of rotation, and $\frac{d\theta}{dt}$ is the angular ...
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Why don't we have 'inverted' atoms with electrons in the nucleus and protons orbiting around? [closed]

I just wanted to ask: What if the structure of an atom was inverted at the level of the charges? I mean that instead of the protons being in the nucleus it is an the electrons that constitute the ...
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Arbitrary frames in special relativity

Consider this quote by James J. Callahan in his book The Geometry of Spacetime where he summarizes the conclusions of his chapter on arbitrary frames in SR (page 165): Once again we find that the ...
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Validity of equipartition theorem and choice of coordinate axis

While reading through the basic derivation of how kinetic energy is related to temperature, I stumbled upon equipartition theorem where $\frac{1}{2}mv^2 = \frac{1}{2}kT$ thus $\frac{3}{2}kT$ in 3-...
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Dervie a lagrangian formulation from an eulerian One

in the solidification of a binary alloy : X18%Y . where the nominal concentration of Y in the alloy phase is 18% , the goal is to determine the variation of < C> ;the average concentration over ...
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Position Operator Eigenvectors change with Space Displacement

I am working through Ch. 3 of Ballentine where he finds the commutator relationships between various operators. He begins on p.78 with a space displacement $$\mathbf{x'} = \mathbf{x} + \mathbf{a}$$ ...
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After what time, the configuration will repeat? [closed]

A ball rotates at a rate $r$ rotations per second and simultaneously revolves around a stationary point $O$ at a rate $R$ revolutions per second $(R<r)$.The rotation and revolution are in the same ...
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Angular velocity in principle axis for free symmetrical top

I'm trying to analyze the free symmetrical top problem by calculating the Lagrangian in the principle axis system. but when I look in the books and try to understand how the kinetic energy was ...
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Centrifugal force in a non-inertial reference frame

There is something I don't quite undestand about the role the centrifugal term plays when describing motion in a non-inertial reference frame. In most Classical Mechanics books, you can find similar ...
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Theoretical question on frames of reference

Some friends (all engineers - not scientists) watching Star Trek and discussing the science behind it. Not whether warp drive or aliens or anything like that were real.... No our discussions were on ...
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Does $F=ma$ still apply when a force creates torque?

Consider a wheel and axle. I apply a force on the edge. That creates a torque. However, why doesn't $F=ma$ still apply? Aren't I still applying a force to the entire wheel/axle assembly, why doesn't ...
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The theorem of the addition of velocities Employed in classical mechanics [closed]

The difference between the addition of velocities in Newtonian mechanics and relativity.
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Tension in a string connecting two masses [closed]

Problem: Two masses $A$ and $B$ connected with an inextensible string of length $l$ lie on a smooth horizontal plane. $A$ is given a velocity of $v$ m/s along the ground perpendicular to line $AB$ as ...
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How do we determine the Center Of Mass (C.O.M.) of a quantum system consisting two particles?

Is it possible to determine the center of mass of a system of 2 or more quantum particles? I recently came across the Feynman Lectures Vol.3 and a particular discussion in the book has spurred up this ...
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Dynamic Modeling of Differential drive 2D robot

Usually Lagrange equations are used for dynamic modeling. In this paper "https://pdfs.semanticscholar.org/4e98/09960be9ec7f1ad8fadf61dad8cb1c8818d0.pdf", the resulting dynamic equations of motion is ...
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How do I choose the correct Lorentz equation for my special relativity problem? [closed]

Lets say There is a moving board moving to the right in the speed of $V = 0.8c\,\hat x$. We know that the angle that the pole creates with the Y axis of our system is 31 degrees $(\alpha = \tan^{-1}(...
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Why do we weigh less on equator when centrifugal force isn't a force at all? [duplicate]

Why would we weigh less on equator as the weighing machine measures the force by which we push ground and that should not change if are on equator or poles?
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Trouble finding the (inverse) transformations between covariant and contravariant components

Consider a point in cartesian and polar coordinates, $P = \{x,y\} = \{r,\theta\}$, such that $x = r \cos\theta$ and $y = r\sin\theta$. I have an arbitrary vector (e.g. a velocity vector) at point $P$,...
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Is there an absurdity in Einstein's equivalence principle? [closed]

A friend of mine, Amir Assarzadeh, upon noticing my thought experiments [1&2], asked me an intriguing question to which he also made an answer defending Einstein's equivalence principle (EEP). ...
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Is quantum gravity consistent with the principles of equivalence and relativity?

I saw an article about physicist testing quantum mechanics in accelerated frames, hoping for insights into quantum gravity. And then I suddenly wondered, is quantum gravity inconsistent with general ...
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From a traveler's point of view, what prevents him from reaching the speed faster than light?

I have read the answer to this question from Eric. That answer is still from the point of view of a standing observer that sees the traveler spending infinite amount of energy. My question is asking ...
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From a traveler's point of view, what prevents him from reaching speed faster than light? [duplicate]

From a traveler's point of view, as he is accelerating with $1g$, in under one year he would reach the speed of light. Note that from his point of view, everything looks normal so he could keep ...
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84 views

Defining Simultaneity

I've been learning about relativity, and I'm just starting to wrap my head around what it means for events to be simultaneous in one reference frame, but not simultaneous in another. Taking as the ...
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Static equilibrium in an accelerated frame of reference [closed]

TL;DR : I'm trying to resolve an exercice of static equilibrium in an accelerated frame of reference but I do not have the same answer as the correction for the rotation equilibrium. We have an ...
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1answer
40 views

Determining the angular velocity from an inertial frame of reference if given a system of two disks stacked

Say I have this disk with radius $R$, mass $M$ that could rotate with angular velocity $\omega_0$ around it's CoM freely (no friction, etc). Then we have a smaller disk with radius $r$, mass $m$ that ...
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58 views

Time period of a simple pendulum in an accelerated frame

Suppose I have a simple pendulum oscillating in an accelerated frame then my textbook says that the time period of the pendulum is no longer given by: $$ T = 2\pi\sqrt{\frac{L}{g}} $$ but by: $$ T =...
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Spin-orbit interaction

When I derived the spin orbit interaction, I switched to the electron's reference frame, so it feels a magnetic field $B$. after calculations I get the spin orbit interaction in the electron's frame ...
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Is temeperature dependent on reference frame?

temperature is defined as the average kinetic of particles and as velocity is relative them the magnitude of temperature must also increase. Is it so? If I move an object/gas container at constant ...
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Gravitationally bound system

I have a question concerning an $N$-body gravitationally bound system. It is quite simple and straight forward but I have not found an answer to it yet. I'm not even sure if the question is actually ...
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A moving object $M$ has the same velocity for both the observer $A$ and the observer $B$

Let $\mathbf{u}$ be the velocity of $M$ relative to $A$, $\mathbf{u'}$ be the velocity of $M$ relative to $B$, and $\mathbf{v}$ be the velocity of $B$ relative to $A$. Then, if $B$ moves away from $A$...
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1answer
34 views

Total work done by friction on a system, when friction is static and internal to system? [duplicate]

Will the total work done by friction on a system be always zero if friction is static and internal to the system? Explain if possible by man boat problem as system and no friction is being provided by ...
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What will be the total work done by friction on the system (man+boat)? [closed]

As I am seeing this, the man and boat will have different displacement from ground frame, so there should be a net work done by friction . The books says, total work done by friction is zero when ...
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Translate inertia tensor, caculate distance matrix

I know that inertia tensor of a sphere is $$ 2mr^2/5\begin{bmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \\ \end{bmatrix} $$ Now if I translate it into a coordinate ...
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2answers
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Is there anything travelling at near $c$? Perhaps $(1/2)c$ or $(3/4)c$? [closed]

There are lots of things traveling at c, light being the most apparent, and gravity, etc. And there are things that travel at very high speed, like binary pulsars that might be moving at 1/4c. But ...
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How do you model the electric field of an electron in motion in a conductor? Is the field given by static or dynamic equations?

It is unclear to me, if an electron in motion in a conductor emits a stationary (Coulomb field) or a dynamic (retarded) field. The motivation for this question, is the following paradoxical ...
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Asynchronous clocks in motion special relativity

I was watching this derivation of 'asynchronous' nature of clocks from which I got slightly confused. Consider two reference frames moving relative to each other call them 'Red' and 'Blue' Frame. ...
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Special Relativity - Events “Coincide” is NOT a relative concept, Why?

Consider 1-D space. Let S and S' be two inertial reference frames. Let A and B be two events. Co-ordinates of A and B under S are A = (xA,tA) and B = (xB,tB). When we say events coincide - it simply ...
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Special Relativity - When events coincide?

Consider 1-D space. Let S and S' be two inertial reference frames. Let A and B be two events. Co-ordinates of A and B under S are A = (xA,tA) and B = (xB,tB). Let me define what I mean by when I ...
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Is comoving coordinate a gauge choice?

Consider the Roberston Walker metric in 4D, $$ds^2 = -dt^2 + a^2(t) \left( \frac{dr^2}{1-kr^2} +r^2 d\Omega^2_2 \right)$$ Now, if we consider the collapse of a spherically symmetric fluid, spherically ...