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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Do blueshifted and redshifted light sources have differing energies?
The thought experiment:
Two spaceships are passing each other some distance from a star. Both ships are at relativistic speed, one toward and one away from the star. Should the total energy observed ...
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Is the age of the universe significantly different as viewed from the Earth's frame of reference than as viewed from the CMB frame?
The standard value given for the age of the universe is 13.79 billion years. But of course, that age depends on the frame of reference; that figure is given from the perspective of the comoving FLRW ...
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Doubt about Lagrangian transformation between reference frames (Susskind, Classical Mechanics, The Theoretical Minimum, pag.117)
I'm working through Susskind's Classical Mechanics book and I reached the point where he explains how to transform the action (and Lagrangian) when changing reference frames. However, I believe there ...
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How is using the principal axis frame in the Lagrangian allowed?
The kinetic energy of a fixed, rotating rigid body is
$$
T =\frac{1}{2}\mathbf{\omega}\mathbf{I}\mathbf{\omega}=\frac{1}{2}I_{xx}\omega_x^2 +\frac{1}{2}I_{yy}\omega_y^2 + \frac{1}{2}I_{zz}\omega_z^2 + ...
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Is modified mass of special relativity inertial or gravitational? [duplicate]
Is modified mass of special relativity
$$m= \frac{m_0}{\sqrt{1-(v/c)^2}}$$
inertial mass or gravitational mass?
I hope $m$ be both of them: we know accelerating massive particles to speed of light is ...
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Rotation of wind in low and high pressure zones
Why do winds rotate counterclockwise around low-pressure systems and clockwise around high-pressure systems in the Northern Hemisphere?
If this rotation of wind is because of the Coriolis effect ...
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Bucket rotated in a vertical plane [duplicate]
This was a "give the reason" question in my textbook.
If a bucket containing water is revolved fast in a vertical plane, the water does not fall even when the bucket is completely inverted.
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Stress tensor transformation in fixed coordinate systems
I have two fixed coordinate systems with different oriented inclined planes and I know components of stress tensor $\sigma_1$ for the first coordinate system.
How to find components of stress tensor $\...
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Ball on semicircular rotating track minimum angular speed
I've had a look on the problem of a ball on a rotating circular track where the ball reaches a stable position at a fixed height that depends on the angular velocity and radius of the track only.
For ...
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A problem with a current-carrying sheet's magnetic field as viewed by an observer moving perpendicular to the current direction (Part II)
Although I have found an answer to my previous question, the problem is still vague for me, as we consider the viewpoint of the observer who recedes from the current-carrying sheet along the $y$-axis. ...
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A problem with a current-carrying sheet's magnetic field as viewed by an observer moving perpendicular to the current direction (Part I)
In my previous question, entitled a problem with a current-carrying wire's magnetic field as viewed by an observer moving perpendicular to it, @Dale answered that:
so indeed, as you mentioned, in ...
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Why is it consistent to apply Newton to non-inertial frames via pseudoforce?
To impose pseudoforce on accelerating frames (step 1), is okay.
But then apply Newton's laws (step 2)— is that okay?
Because it deems the modified frame as inertial (necessary for application of our ...
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How to define inertial reference frames in classical mechanics using the Lagrangian and Hamiltonian formalisms?
Using the Newtonian formalism of classical mechanics, an inertial reference frame is defined as one where changes in the motion of an object can only be caused by a force acting on it. What would the ...
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How to prove that intrinsic quantum spin is invariant under change of rotation frames?
We know that quantum spin is invariant under change of inertial frames. How do we know that they are invariant under change of non-inertial frames? From a non-rotating to a rotating one?
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For a body undergoing Born-rigid motion, is there always an inertial frame in which it is entirely at rest?
Roughly speaking, a body is said to undergo Born-rigid motion if the distance between any two "infinitesimally separated" points in the momentarily-comoving inertial frame (MCIF) of either ...
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Doubt about torque and axis/point of rotation reference system
I'm having difficulties seeing when I can "rotate" the reference axis in a torque problem and when I cannot. Let me illustrate it with the following problem.
I have the following system:
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Why can the point of application of a force be moved along its line of action in a rigid body?
I can't find a proof for the following statement:
In a rigid body, the point of application of a force can be moved anywhere along its line of action and its effect will remain the same.
Do you know ...
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Definition of spatial twist of a rigid body
I am learning about spatial twist $\mathbf{V}_{AB}^s$ from MLS(A Mathematical Introduction to Robotic Manipulation). MLS defines the linear component of spatial twist defined as:
$v_{AB}^s$ is the ...
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Object in non-inertial frame can have zero net force $F=0$ but non-zero acceleration $a≠0$?
I watched this video about inertial vs non-inertial frames, at 3:30, professor say particle has zero net force ($\mathbf F=\mathbf 0$), but non-zero acceleration ($\mathbf a≠\mathbf 0$).
But particle ...
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Why does the bar in the gym not fall when one side is loaded with weight?
Lately I observed that the bars that is used to do bench press in gym don't immediately fall on the side loaded with weight. Which does not sound correct intuitively, the bar should fall down because ...
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Does magnetic field vary when frame of reference changes?
This question comes from a photo of my homework. There is a light stick with two balls on both side. I've balanced the weight of them so they could rotate freely around the point O. The ball on the ...
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Is Newton's first law based on inertia or frame of reference? [duplicate]
Our Physics Sir in class said that the first law isn't law of inertia..
I asked for clarification but he only said its based on frame of reference. Till now, we were always taught that Newton's First ...
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Does fixing a $z$-axis and state also fix other coordinate axes in quantum mechanics?
Say we have an EPR pair $|\psi\rangle := (|00\rangle + |11\rangle)/\sqrt{2}$, where $|0\rangle, |1\rangle$ denote the Z-axis eigenstates of, say, a spin-1/2 particle. We measure both parts of the ...
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Are center of rotation and center of mass are same for an ellipsoid falling in water under gravity?
Consider an ellipsoid solid freely falling under gravity in water. The solid is free to rotate and translate inside water. If gravity is the only force acting, I understand that center of mass and ...
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Is angular momentum balanced locally?
So consider the balance of angular momentum for a system of particles
$$ \sum r_i \times F_{iext} = \frac{dL}{dt} \tag{1} $$
If no external forces are present, RHS vanishes, and thus, that implies ...
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