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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In zero gravity!
If a spacecraft moving in a stable speed or acceleration and suddenly stopped did a astronaut will continue moving forward ( such as a man in a train) ?
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Exact difference between '''Fermi normal coordinates''' and ''Riemann normal coordinates'''? [duplicate]
I want to know the exact difference between '''Fermi normal coordinates''' and ''Riemann normal coordinates'''?
Here is a same question, but it's hard for me to understand.
Difference between Fermi ...
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If universe is expanding then relative to what? [duplicate]
I am very keen about the fact that universe is expanding.If something expands, it expands relative to something else. If the universe is expanding, then it must expand relative to something else. What ...
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Parallel Axis Theorem and Kinetic Energy of the Earth
I'm looking for a little clarification on the parallel axis theorem and computing the total kinetic energy of the Earth in it's orbit round the Sun.
So the Parallel Axis Theorem states that $I = I_{...
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1answer
26 views
Light speed in vacuum over space and time [duplicate]
Is the light speed the same, constant, in all the universe locations?
I mean, is it he same in the surface of the Sun compared with speed in space inter galaxies?
Also: is light speed now the same as,...
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The spring paradox: Is there any rational transformation for the relativistic force?
A simple thought experiment crossed my mind a few years ago for which I could not as yet find a convincing answer:
Assume that a mass-less spring $S_1$ with (proper) constant $k_0$ hangs from the ...
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Which are the Physical (Not Mathematical) Axioms of General Relativity? [duplicate]
I have an idea on what the correct answer may be.
The first axiom is the axiom from Special Relativity. The laws of Physics apply identically to inertial frames of reference. This axiom contains the ...
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1answer
66 views
Change of reference frame for a wavefunction: same modulus but different currents?
Suppose that, at a certain $t=0$, one has a wavefunction
$$
\psi=\psi(x,y)
$$
defined on a plane and well normalized to $1$. Coordinates (x,y) refer to the frame $xOy$.
How does the wavefunction ...
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2answers
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Why can't we take space as universal frame of reference?
Suppose we have a ball filled half with water in space with nothing else around (nothing else in the whole space except the ball) and suddenly it accelerates for time t. obviously, there would be ...
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Moment of inertia “about ? axis”
I'm just trying to calculate how fast a 2D polygon should spin given x amount of energy. To do this, I figured I'd split my shape up into triangles, calculate the MoI for each around the polygons ...
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3answers
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Difficulty in understanding why a car slips towards outside as seen from inertial frame
While turning on a road, why does a car slip towards outside, if we are observing the car from inertial frame of reference, i.e center?
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Euler force for pendulum
Hello I have a question related to the Euler force. Why is this force never considered for a simple pendulum?
As far as I understand, Euler force is given by (assume I would consider the 2d pendulum ...
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Find rotation points on an object given a center of rotation in other
i have 3 objects, n1 has to rotate from position a to position b, using as pivot point a given one on object 2 (the yellow one).
To do that i need to use a 3rd object n3 that can be of the lenght i ...
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1answer
461 views
Why does the Coriolis force appear when deriving the forces on a particle in polar coordinates?
I considered a particle in polar coordinates, $(r,\theta)$, with mass $m$. The standard basis vectors in polar coordinates are:
$$\mathbf{\hat{r}}=\cos{\theta}\mathbf{\hat{x}}+\sin{\theta}\mathbf{\hat{...
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1answer
47 views
Can we move without moving? [duplicate]
So here is the question,
If I jump and hover over the ground for sometime why don't we move away from the point I jumped from? Because earth is rotating so if I hover long enough we should move from ...
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3answers
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Work associated with pseudo force
In a non inertial frame if I want to apply the Newton's laws of motion one would use the help of pseudo force but in non inertial frame if I try to apply the work energy theorem should I consider the ...
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Centrifugal force and centripetal force in fixed coordinate frame
Hello I have a question related to centrifgual force. So in basic textbooks the movement of a particle in a rotating coordinate frame is derived. A starting point is to consider a fixed and a rotating ...
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1answer
47 views
What is tension in cabel of elevator? [closed]
A block of mass $m$ is kept on the floor of an elevator of mass $M$ and the system is accelerating upward with acceleration $a$. The acceleration due to gravity is $g$.
$F_n$ is Normal force on Block.
...
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Relativistic mass effect
Does relativistic mass phenomena only appear while accelerating or even when the object is travelling at constant velocity (say 90% speed of light)?
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2answers
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Meaning of the term speed of light in context of an object of non-zero mass
We know from GR that an object of non-zero mass cannot propagate at light. I have a problem with the term speed of light. Does it mean the relative speed of that object with another object or frame of ...
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1answer
27 views
Relative angular velocity
Two bodies are in circular motion with A at one diameter and having velocity tangentially downwards and B at other end of diameter tangentially upwards. Find angular velocity of particle A wrt B if ...
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2answers
140 views
Hypothetical effect of Solar System/Orion Spur traveling near speed of light
I was hoping that some genius could explain what we would observe in the universe around us in the following hypothetical scenario in which the earth itself were traveling at or near the speed of ...
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3answers
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Special Relativity - Clock Synchronization
In Special Relativity - Is their a definition of "synchronizing" clocks which are moving relative to each other?
I suspect such a definition makes no sense - as moving clocks belong to separate ...
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Fixed coordinate frame as limit of rotating coordinate frame
I have a question about a fixed coordinate system as limit of rotating system. Consider for example a pendulum. The Lagrangian in the rotating frame is given by
\begin{equation}
L(\mathbf{r}, \mathbf{\...
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Does all objects really fall with the same acceleration? [duplicate]
I know that acceleration due to gravity is independent of mass :
$$a = \frac{F}{m} = G\frac{M}{r^2}$$
Meaning that a hammer and a feather fall with the same acceleration on the moon.
I am confused, ...
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If absolute velocity does not exist, how can we say a rocket accelerates in empty space?
If a rocket in space fires its thrusters, it is propelled forwards as per the laws of motion. This can be measured by its position relative to other bodies in the universe.
Hypothetically if there ...
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2answers
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Special Relativity - Reference Frames $S$ and $S'$
Consider the standard arrangement in special relativity.
Let S' move in the +ve x-axis with a velocity V with respect to S
Question: S then moves with a velocity -V with respect to S'.
Is this an ...
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Lagrangian of free particle in non-inertial frame
As in Landau & Lifshitz 1st chapter
"If an inertial frame К is moving with an infinitesimal velocity e relative to another inertial frame K', then v' = v+e. Since the equations of motion must ...
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0answers
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Angular momentum and external torque
In John Taylor - Classical mechanics it was mentioned that the equation
$L' = \Gamma^{ext}$
is true even with respect to the center of mass. Here we are working with a system of particles, $L = \sum ...
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3answers
138 views
Why cannot we determine our own velocity?
I know it would violate the principle of relativity. But have there been serious experimental attempts to contradict that principle?
If I am in a moving train without windows and totally sound proof,...
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1answer
71 views
What physical quantity remains equal in different frames? [closed]
I recently came across a problem which involved going into rotating frames. And it was pretty tiring. (And difficult..). So I wondered if there was some quantity that you could measure from the ground ...
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1answer
39 views
Velocity of particle in non-inertial frame [closed]
Can velocity of the free particle remain constant in non-inertial frame as contrast to free particle in an inertial frame?
I know the answer is straightforward yes but taking a different perspective ...
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Lagrangian in non-inertial frame
Does Lagrangian in non-inertial frame may/may not depend on coordinate but always has to dependent on velocity and time for free particle in contrast to inertial frame where lagrangian is always ...
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3answers
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Kinetic energy of an object
We know that motion is relative. So let an object(o) be moving with a certain velocity with respect to an object (A).If another object (B) is moving with respect to (A) at a given moment and they ...
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How would an observer extremely close to light speed perceive (experience) the universe?
In the following we consider an Earth bound reference frame.
For an observer very close (but under) the light speed, radiation from the universe would emanate from a single point in the direction of ...
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2answers
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Conservation of Angular Momentum w.r.t a Reference point
When angular momentum is conserved, does it mean that it does not matter what the reference point is at? Say for example with this image below, the observer stands at two possible points P1 and P2. ...
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Why doesn't the Earth's acceleration towards the Moon accumulate to create noticeable motion of the earth, towards the moon
I get that Earth's mass is very large, so its acceleration is very tiny. But wouldn't the acceleration accumulate over a period of time and become noticeable?
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3answers
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Force exerted by rails on a high speed train
I need to find the ratio between horizontal and vertical accelerations exerted on a train by the rails it is running on , given that the train is traveling East at a speed of $v_r=250$ km/h, along the ...
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3answers
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Rotational velocity necessary to make apparent weight equal to “real” weight?
I have been trying to find a solution to this, but I never reach same one that my professor provides. The problem is the following:
For an object of mass m standing still on the surface of the ...
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1answer
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Difference between coordinate systame and frame of reference in relativity
I have taken a relativity course, and am not quite clear as to whether the notion of a frame of referene is independent of the coordinate system. At the moment, I think that any frame of reference (of ...
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1answer
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Speed of light in vacuum in non-inertial frame [duplicate]
Does the speed of light remains $c$ also in non-inertial frames? Or it changes from frame to frame?
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5answers
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Why haven't we yet tried accelerating a space station with people inside to a near light speed? [closed]
Is that something we could do if we use ion or nuclear thrusters?
Wouldn't people in the station reach 0.99993 speed of light in just ...
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1answer
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Boost as a generator of constant acceleration
In Covariant Loop Quantum Gravity by Carlo Rovelli p204, Sec 10.4, there is a paragraph which states
..., a trajectory at constant acceleration is generated by the boost
generator $K_z$ in the ...
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1answer
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Would conservation of angular momentum make it difficult to fall sideways in an O'Neill space colony?
It's always bothered me that the O'Neill space wheel puts forth centrifugal force as a suitable replacement for gravity. However, it seems the effects of conservation of angular momentum would induce ...
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1answer
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Accelerated frame vs gravity frame
Can accelerated frame change curvature of space as gravity does?
Can there accelerated frame be pure inertial frame?
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2answers
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Inertial frames as in Landau & Lifshhitz mechanics 1st chapter
If we see inertial frames from a basic point of view (precisely more basic axiom from which I can at least derive the law of free body as in landau mechanics first chapter) that inertial frames are ...
2
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2answers
159 views
The Earth revolves around the Sun or the Sun revolves around the Earth
Well, in today's world we know that the earth resolves around the sun. But that is seen from frame of reference of sun or an observer stationary wrt sun.
From frame of reference of the earth, sun ...
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Coordinate transformation of basis vectors
The question
Let $e_a$ be the coordinate basis vectors in a manifold described by coordinate system $x^a$. The vector displacement between two nearby points is given by
\begin{equation}
ds=dx^ae_a=dx'...
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1answer
100 views
How slow can time get near a black hole?
The closer I get to a black hole, does time slow down proportionally?
Does time stop near the event horizon?
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1answer
60 views
Calculating acceleration of end point of rod
Suppose I have a rod hinged at its end, of length $\ell$ free to rotate about an horizontal axis; initially in the horizontal position and I have to calculate the acceleration of its other end point. ...
