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 dentoe particular coordinates chosen on the spacetime manifold.

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Turning off point for 1g acceleration

Let's say I am on a ship accelerating with 1g. I want to keep the engine running for half a year ( to an observer from my point of origin ) but due to time dilation it would have to be sooner than ...
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Twin paradox, different starting locations

Let's say I have a twin who is at rest relative to myself and ten light years away from me, we are both in rocket ships. We have agreed that I will send a laser pulse and that when he receives it we ...
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Momentum in the frame of reference of the center of mass [on hold]

I'm a high school student who just learned this topic in class today. I don't understand why the sum of momentum is zero in the frame of center of mass. Also, how can I solve this problem: Three ...
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Angular Momentum conservation in star system

This question is related to what happens to a planetary body(like earth) when the star it is orbiting collapses under its own gravity. Suppose a star is rotating about its axis with some angular ...
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What are galactic speeds measured against?

The Earth moves through space at 67,000 MPH. The Milky Way travels through a local group at 2,237,000 MPH. Wouldn't you need a fixed point to be able to measure velocity against? After all, compared ...
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21 views

When conserving angular momentum, about which point(s) should it be calculated?

In my physics problem I have a ball fired at a non fixed bar, which is moving at some velocity, causing them both to stick together and the bar-ball pair to rotate about the new center of mass. About ...
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103 views

Schroedinger Equation and Special Relativity

From what I understand, the Schroedinger equation describes how the wave function of a quantum system evolves in space over a given time (I am referring to a relativistic version of the Schroedinger ...
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1answer
23 views

Rotational dynamics about a point or an axis?

In several books and sites, its written that torque is calculated about an axis and angular momentum is calculated about a point. In MIT's Angular momentum lecture pdf, Angular momentum has been ...
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Period of a pendulum in a lift going up [duplicate]

So I know that the period of a pendulum in a free falling elevator isn't going to change because there is no force acting on it since $$T = 2\pi\sqrt{\frac{\ell}{g}}.$$ So what happens to a pendulums ...
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13 views

Determine coordinate system for rotating wheel

I am having trouble writing down the coordinate systems for a problem. In particular, I'm not sure how to figure out the translational acceleration of the moving coordinate system relative to the ...
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Can I choose any reference frame? [duplicate]

I'm a horrible noob at anything past mechanics, so please bear with me. According to Einstein's theory of relativity (at least as it is known in "popular science" (lowercase)), mass-full objects ...
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1answer
108 views

Time dilation - Earth & Jupiter [duplicate]

I have this doubt after watching Interstellar movie :) Lets assume I am in Jupiter. (I know it is a gas planet, full of hydrogen and helium, has extreme pressure etc. Lets please ignore those facts ...
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3answers
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Intuition and difference between centrifugal force & Coriolis force?

My book says that when a frame rotates uniformly, pseudo/fictitious force must be taken to count. This is centrifugal force. Also, while Googling, I found another pseudo force Coriolis force. ...
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Relative time dilation in Schwarzschild metric

Let's say we use the Schwarzschild metric to model the curved spacetime around a planet of mass $M$ and radius $R_0$. One clock $A$ is hovering at distance $R_A$ > $R_0$ with the help of rockets, a ...
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2answers
77 views

Consistent answers in special relativity [closed]

I was doing a question about if a train fits in a tunnel. From the train frame it does not and from the tunnel frame it does. Then the question asked are these two answers consistent? What does this ...
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0answers
17 views

How to prove the relation between the rate of change of a vector in space coordinate and in body coordinate?

I'm learning Goldstein's classical mechanics, and in chapter 4.9 he prove such an operator equation $(\frac{d}{dt})_s=(\frac{d}{dt})_r+\omega \times$ In the proof, he takes the space and body axes as ...
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Is there a preferred reference frame?

At any point in space there is only one truly inertial frame (the one that is in free-fall under local gravity conditions), does this form a preferred frame of reference? Special relativity tells ...
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31 views

How does an observer in arbitrary state of motion assign numbers to events in a flat spacetime?

In a flat spacetime, there is an inertial observer, who assigns events coordinates in a usual fashion: Placing a clock everywhere and synchronize them. From his POV, the other observer is moving in ...
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Why is $\mathbb{R}^1$ different than Euclidean space $\mathbb{E}^1$? Roger Penrose road to reality

In Roger's book, the following is stated: (I'm paraphrasing because my book is in spanish) "We consider time as part of a space, namely $\mathbb{E}^1$, instead of it just being a copy of the line ...
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4answers
71 views

Why is coordinate time frame dependent? [duplicate]

Here is what I understand by coordinate time. It is the time difference measured between two events, using two synchronized clocks, one present at each event, and the difference is measured in an ...
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2answers
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Why does time slow down when traveling at high speeds [duplicate]

One of the effects of traveling at high speeds is slowing down of clocks. I can understand gravity time dilation effect but not how would velocity affect clock speeds. How correct it is, if I say ...
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2answers
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How velocity dispersion changes with change of inertial frame

I'm analysing a bunch of simulated galaxies, and one of the properties I'm looking at is their velocity dispersion (which is the same thing as the standard deviation of their speeds as far as I know). ...
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Is uncertainty in velocity via HUP reference frame dependent? [duplicate]

Simply put HUP involves position and momentum, further more consider a mass of 1kg. as momentum is mass X velocity = 1X velocity = velocity for calculation purposes. now for a stationary observer the ...
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Why does rotation simulate gravity if motion is relative?

In Einstein's theory of relativity, if motion is truly relative, then why would somebody in a rotating space station experience (artificial) gravity? I mean, I get why they experience gravity IF the ...
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2answers
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If a photon is exists in 'timeless' state, how can objects around it move? [duplicate]

My understanding is that light does not experience time. In attempting to understand what the universe would be like from the perspective of a photon, the answer I get is that the universe would be ...
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How to understand non-associative composition of velocities in STR?

In STR the composition of non parallel movements is in general non-associative. The formula is $\displaystyle\bar{u}\oplus\bar{v}= \frac{\bar{u}+\bar{v}_{\|}+\bar{v}_\bot/\gamma}{1+\bar u\cdot\bar ...
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Time should run slower near massive body

We have considered that time should run slower near massive body like Earth, BH. There is no gravity in space, means time is faster in space compare to earth. Then How is it possible that man who ...
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Can all fundamental forces be fictitious forces?

After reading many questions, like this and this, I wonder: is it possible to consider also the other fundamental forces, the electroweak interaction and the strong interaction or ultimately the ...
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1answer
36 views

When you are standing in a running train if you jump means will you be in same place or will you be in front or back? [duplicate]

When you are standing in a running train if you jump means will you be in same place or will you be in front or back?
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Center of mass of two $\gamma$ rays moving in opposite directions

Suppose there are two $\gamma$ rays with frequencies $\nu_1$ and $\nu_2$ moving in opposite directions according to a reference frame $S$. I want to find the velocity of the center of mass of this ...
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Mach's principle in empty universe, centripetal force and violation of Newton's laws of motion [closed]

Questions about Mach's principle and empty universe has been asked many times but nowhere can I find it's cross examination with centripetal force. From my point of view the simple logic of ...
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1answer
71 views

Can we measure kenetic energy on an absolute scale, or does it have to be measured with reference to something else?

I recently read the question Kinetic energy of an object at rest where it was suggested that the kinetic energy of an object on Earth is measured in the reference frame of Earth. Can we measure ...
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Kinetic energy of an object at rest

Why don't we consider that an object on Earth has kinetic energy as it is also moving at the rotating speed of Earth?
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Explanation for “if all accelerated systems are equivalent, then Euclidean geometry cannot hold in all of them”

I'm doing an EPQ (mini college research paper) on gravity, and I found a site that explained things in simple terms. I am having trouble understanding how Einstein came to his revelation space-time ...
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Applying Lorentz Transformations and Time Dilation

My question is based on a popular question, usually posed in introductory courses on the special theory of relativity. Two rockets are on a collision course. Rocket 1 is traveling at the speed ...
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9answers
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Physical meaning of the angular momentum

Still reading Classical Mechanics by Goldstein, I'm struggling on a very basic notion: angular momentum. I physically understand it as the momentum of an object rotating around something given a ...
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2answers
73 views

Who plays the role of centrifugal force in an inertial frame of reference?

It is noteworthy to quote a sentence from my book, It is a misconception among the beginners that centrifugal force acts on a particle in order to make the particle go on a circle. Centrifugal ...
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Measuring speed of the moving train, if I'm inside it

So I am inside a coach in a train that is fully sealed (with no windows and a locked door). I have a torch, photo & time sensor and a scale with me. So, I place the sensor at one of the walls and ...
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2answers
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If the vacuum is not “emptiness” why the speed of the electromagnetic wave is independent of the frame of reference?

If the vacuum were "emptiness" it were easy to accept that there is no "preferred frame of coordinates" and the light velocity is the same in any inertial frame of coordinates. But the vacuum is an ...
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Does space between objects contract?

I had a question, let us assume a coordinate system where there is 2 objects moving at relativistic speeds (at same velocity) for the observer therefore the observer will observe the length ...
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Does mass increase at relativistic OUTSIDE of the mass's frame of reference? [duplicate]

There are other questions on here with responses saying that the mass does not change from its own frame of reference. But those answers were somewhat unclear if the mass changes to someone observing. ...
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How would we explain meteorological phenomena in an inertial reference frame?

The Coriolis effect is used to explain the formation of typhoons, hurricanes, and cyclones and other phenomena where we take the Earth as a rotating reference frame. How could we explain this ...
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Hardy's paradox (see the article “Quantum Mechanics, Local Realistic Theories, and Lorentz-Invariant Realistic Theories”)

Does this thought-experiment (Phys. Rev. Lett., Vol. 68, No. 20, page 2981, year 1992) represent a proof against Bohm's interpretation of the quantum mechanics? The analysis of Hardy rules out local ...
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How to know if a vehicle is moving without any external source of information?

The situation is the following: I'm inside a vehicle (plane or a car, it doesn't matter) and I need to know if the vehicle is moving at a constant speed BUT I cannot perceive any external change like ...
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Two referential frames. An ant is moving on a uniformly rotating disk and appears not to be moving relative to the disk [closed]

They want us to find the Coriolis and centripetal acceleration. My problem is drawing the referential. Because, there are 2 referential frames. The inertial one would be the disk right, with 3 axes, ...
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1answer
115 views

How to explain centripetal force in terms or relativity

At the end of a video of dropping a ball and feathers in a vacuum, Brian Cox explains that the Ball and Feathers, as understood in terms of General Relativity, aren't falling. (apologies I can only ...
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5answers
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High speed does not kill. Does acceleration do it ? or jerk?

In a recent question the OP asked why high speed will not kill us. The accepted answer, highly upvoted, stated very first that Speed doesn't kill us, but acceleration does. The second answer ...
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Relative velocity of two objects travelling at $c$ (or near $c$) [duplicate]

If two bodies are travelling at speed $0.9 \, c$ in opposite directions, what will be the speed of one, as observed by another? Newtonian mechanics won't apply at such speeds. As such, how will we ...
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Question on using Transport Theorem to Determine Angular Acceleration of a Rotating Frame

My question is regarding using the "Transport Theorem" on the angular-velocity vector of a rotating frame itself. Suppose: Frame-F has basis vectors I, J, K. Frame B is rotating with respect to F ...
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Choice of the z-axis in the Schrödinger equation for the hydrogen atom

I am reading about the solution of the Schrödinger equation for the hydrogen atom and have a question about the choice of the z-axis. Most websites say that the z-axis is arbitrarily chosen. If so, ...