# 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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### 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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### 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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### 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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### 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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### 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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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 ...