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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Application of Reichenbach synchronisation
Suppose I adopt the Reichenbach synchronisation process so that light heading radially away from me- according to my clocks- travels with infinite speed, while light heading directly towards me ...
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How does the concept of "coordinates" makes sense when considering large scales of the universe?
I will describe two instances, that led me to ask the question of relevancy or meaningfulness of coordinates when we are not local in our observation of the universe, but rather we consider a large ...
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Proof and meaning of $\vec{v} = \vec{\omega}\times\vec{r}$
Elementary question but I'm slightly confused about the statement $$\vec{v} = \vec{\omega}\times\vec{r}.$$ I know that $\vec{\omega}$ is simply the time derivative of $\theta$, which, to make things ...
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Has someone ever obtained a relative trajectory being exactly the Coriolis formula without a background centripetal force (as gravity)?
In geophysics and many other cases, the Coriolis formula is clearly linked to a background centripetal force.
Read Anders Persson (UK MetOffice, EU ECMWF, Sweden SMHI, Uppsala) https://scholar.google....
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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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What force(s) is rotation made of? [duplicate]
Can the rotation of an object be viewed as the result of two perpendicular forces ('push' and 'pull') that have combined? When I spin a wheel there is a 'push force' at a right angle to the wheel's ...
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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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Clock on a moving rocket
Let's say that there is a clock mounted outside a rocket that is moving at a constant velocity upwards as measured by an adjacent observer looking at the clock from a stationary platform. The clock's ...
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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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Equivalence principle and principle of relativity
If equivalence principle was not true could we have almost inertial reference frames near the earth? Specially, is it was possible for a person in a train to know that if it is standing still or it is ...
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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
$$
T =\frac{1}{2}\mathbf{\omega}\mathbf{I}\mathbf{\omega}=\frac{1}{2}I_{xx}\omega_x^2 +\frac{1}{2}I_{yy}\omega_y^2 + \frac{1}{2}I_{zz}\omega_z^2 + ...
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Will a Coin rotate always about its diameter/com when Tossed?
When a coin is tossed in the air by applying an impulse at some distance from the Centre of Mass (centre of ring), it will start rotating and move up vertically as well.
Can we say that the coin will ...
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Is modified mass of special relativity inertial or gravitational? [duplicate]
Is modified mass of special relativity
$$m= \frac{m_0}{\sqrt{1-(v/c)^2}}$$
inertial mass or gravitational mass?
I hope $m$ be both of them: we know accelerating massive particles to speed of light is ...
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On the meaning of the radial coordinate in the simplification of the Two-Body Problem. Inertial or non-inertial reference frame?
When presented with the two-body problems, we usually start from Newton's 2nd equations for the two bodies:
$$
\begin{split}
m_1 \mathbf{\ddot{r}}_1 &= f(r) \mathbf{\hat{r}}, \\
m_2 \mathbf{\ddot{...
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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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Principal axis of circular disc with removed circular portion [closed]
From a circular disc, a circular portion of radius R/2 has been removed....it is asked if the axis YY' is principal axis or not...so my first intuition was since the axis is not symmetric this should ...
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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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Gravitation, infinite series of objects with ever increasing mass & distance [closed]
This might seem like a homework style question but it is not so, my question is:
let there be infinite objects arranged in a line, with increasing mass and distance respectively, you may take any ...
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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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Effect of Sun's gravity on an object on the Earth's surface
Can you please explain why we often don't consider force due to the Sun's gravity on an object on Earth?
(The relevant topics that I am referring to are frame of reference and free body diagram.)
Is ...
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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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Steve Mould's turntable paradox confusion
In Steve Mould's turntable paradox video (time 2:08 to about 2:50) he places a pool ball on a turntable while gently holding it in place allowing the ball to get up to the same speed as the turntable, ...
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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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Help understanding moment of inertia [closed]
I'm learning about moment of inertia for the first time in the prep work set by my university before term starts (I'm going into first year in a few weeks). And as I understand it, it's basically the ...
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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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A problem with a current-carrying wire's magnetic field as viewed by an observer moving perpendicular to it
Resnick argued the motion of a charged test particle at rest relative to a current-carrying wire from the viewpoint of the electrons and protons inside the wire in his book, Introduction to Special ...
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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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Instantaneous axis of motion
I'm currently studying rigid body kinematics, I'm using a book called "Analytical mechanics" (translated from italian) by Fasano and Marmi. In section 6.3 it is told the following theorem:
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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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Symmetrical Twin Paradox [closed]
Suppose twins A and B leave Earth in two rockets, each accelerating at 9g until reaching 0.5c.
Then twin A slows down at 9g and immediately returns, accelerating at 9g until reaching 0.5c, and finally ...
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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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Impulse applied to the wall with my hand but why isn't there a change in the momentum of the wall?
If I am pushing my hand against the wall for a long time am I applying an impulse? While pushing against the wall I am preventing my center-of-mass being moved by also pushing my feet against the ...
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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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Can we figure out the acceleration of a freely falling frame?
So basically I am undertaking my first course in General Relativity and my instructor told us about the need of defining a "Local inertial frame" in GR. His argument was something like this :...
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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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What is the motion of a thin rod if there is a constant force acting perpendicular to it? [duplicate]
Consider a rod of uniform density floating in space, with an inertial observer initially at rest relative to the rod.
If a constant force is applied at one end of the rod (always perpendicular to the ...
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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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Change of rotation axis for an isolated rigid body [duplicate]
Can rotation axis of an isolated rigid body (keeping its angular momentum) change direction without external forces?
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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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Gravity same as free space?
Einstein’s remarkable insight was that a man falling freely experiences no gravity and his experiences are identical in some sense to a man far away in free space.
But the man falling is increasing ...
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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 should components of force be independent?
I read in some sources that components of force should be perpendicular and thus independent.
Why should components of force be independent? Is this always the case?
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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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In what situations may we use the center of mass for calculations?
On the Wikipedia chapter on the center of gravity, there is a calculation that shows that the center of mass is a point about which a uniform, unidirectional gravitational force does not cause torque.
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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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Interpretation of the lorentz-invarient transition rates (LI Fermi's Golden Rule)
As I'm studying for my particle physics exam I have noticed that I do not know how to interpret the lorentz-invariant Fermi's Golden Rule. Or more precisely the transition rate $\Gamma_{fi}$.
For ...
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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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Advantage of launching a rocket from the Equator
I have recently read the following in a book:
As a result of the Earth’s rotation, objects on its surface would be
flung off were it not for the Earth’s gravity holding them down. In
fact, this “...
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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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Can a photon be gravitationally redshifted if it has no mass?
Gravity affects all energy, including photons, but what’s actually happening to a massless particle as it climbs out of a gravity well? Does its wavelength “stretch” in transit, or does spacetime ...
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