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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Simple Relativity Question [on hold]

I've been taking a course in modern physics and we've spent several weeks on relativity now, but I still am confused how to deal with this problem, which has shown up in several different ways ...
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A few questions on passive vs active Lorentz transformations

1.) How do we physically interpret an active Lorentz transformation? The passive transformation seems simple enough: you view a fixed object from the perspective of a new observer. When we actively ...
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64 views

Time Dilation Problem [on hold]

I'm having some trouble using the time dilation formula. Say an astronaut leaves Earth for 10 years, at 0.85c. How much time has passed according to an observer on Earth? I tried using the ...
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Should I abandon my thought experiment about time?

I'm trying to think about special relativity without "spoiling" it by looking up the answer; I hope someone can offer some insight - or at least tell me I'm wrong. Suppose I have an ordinary clock ...
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79 views

Don't Inertial forces obey Newton's third law? [duplicate]

I read in a book (Fundamentals of Mechanics by IE Irodov) that inertial forces do not obey newton's third law. I am unable to imagine and get this in my mind. It states: "Inertial forces are not ...
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85 views

How can one always be standing still when compared to the speed of light?

I was thinking if I built a device with 7 clocks, synchronized to each other, one in the middle, one up, down, left, right, behind and in front of me, say 1 meter away, and I fired a laser from the ...
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If everything is relative to each other in this universe, why do we keep the Sun to be the reference point?

and study the solar system and universe relative to it and why not relative to the Earth?
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Refractive index of dielectric in different frames of reference

The setup A transparent isotropic dielectric medium moving in the negative $x'$ direction at speed $v$ in frame $S'$ is stationary in frame $S$, where it has refractive index $n$. In other words, ...
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Coulomb's Law- Why the Coulomb's law is valid only for point and static charges?

Why the coulomb's law is valid only for point and static charges? Is there is any definite reason?
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67 views

Why doesn't a car slide down a banked road when there is no friction?

In case of banked roads without friction, there is an additional $mg \sin(\theta)$ which is unbalanced. Why isn't this taken into account because it is responsible for making the vehicle slide down ...
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28 views

Pseudoforce and friction: confusion

Consider the following situation. A block of mass $M$ is resting on a rough horizontal ground, and a frame is moving towards the right horizontally with an acceleration $a$. Suppose the coefficient of ...
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Question about Origins in Galilean transformation

I'm just learning about relativity, and every equation I see for a galilean transformation of frame $S'$ (moving with uniform velocity in the $x$-direction with respect to frame $S$) is $x'=x-vt$, ...
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99 views

What distance does one travels in his lifetime? [closed]

I think this isn't answerable without having point of reference from which speed at which earth travels in space, however if I am wrong the please give absolute distance. Considering that earth spins ...
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Perceiving travel speeds from different view points

Scenario: Two vehicles pass each other on a highway moving at 100km's an hour; from a stationary position beside the road you witness these cars pass each-other directly in front of you: from your ...
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Foucault pendulum initial velocity

This is a basic question I can't solve and it seems it is not addressed on the web. Sorry for my lame painting skills. Assume we have a foucault pendulum suspended in the north pole. the pivot is ...
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2answers
79 views

Inertial frames

I'm just starting my study of relativity, and I have a rough understanding of the connection between inertial frames, newton's laws, and galilean transformations, but I'd probably benefit more if ...
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2answers
60 views

Conservation of energy in a different frame of reference

Consider a rollercoaster that goes down a slope: At the higher level it has speed $v_0$, then it goes down a slope and at the end it has speed $v_0 + \Delta v$. The carriage is not powered and has ...
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4answers
115 views

What do you exactly mean when you say that momentum is conserved?

I am taking for granted that when we say that something is conserved it is understood 'in its full integrity'. Energy is represented by a number (of J, or other) and is usually conserved. But ...
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1answer
62 views

Conservation of linear momentum, when is it conserved?

Will Linear momentum be conserved in a non-inertial frame of reference? In other words what is the fundamental condition for linear momentum to be conserved? Also which is more fundamental- Newton's ...
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1answer
331 views

Centrifugal force affecting satellite

I'm trying to explain the behaviour of a geostationary satellite using different frames of reference. Inertial frame: The satellite has a circular motion with angular velocity $\omega$. The ...
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Gauge formalism in rigid body mechanics

When doing calculations in rigid body mechanics, it is necessary to choose an origin to calculate torques and angular momenta. However, the underlying dynamics does not depend upon the choice of that ...
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69 views

Rotation from Goldstein's Classical Mechanics

I apologize for the ambiguity in my title. It was rather difficult to figure out what is the most appropriate title for my questions. My questions come from chapter 4 and chapter 5 of Goldstein, ...
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Is “now” or “the present moment” properly defined in GR?

My question is about the extent to which "now" is defined in GR. In Minkowski spacetime, it's possible to define a "now" for an inertial observer by finding a spacelike 3-plane such that, in the ...
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3answers
151 views

Does this count as moving faster than light?

I'm not familiar with any complicated physics equation, however I do understand some basics. Suppose there is two objects, both of them are moving away from each other in a 3-dimensional space, which ...
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2answers
85 views

How do we know that clocks slow down relative to each other? [duplicate]

For example if a body in motion experiences time dilation, why does it see a body at rest slow down relative to it? wouldn't it make more sense if the body at rest has a faster clock relative to it?
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Magnetic force and relative frame

The magnetic field for to a moving charge depend on its velocity (Biot Savart's law). My question is that is it then not frame dependent? If it is, it means if a man is walking and other is standing ...
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Is centrifugal force equal in magnitude to the centripetal force in the frame of a body undergoing circular motion?

I was working out the minimum tangential velocity required for a swing to complete a full revolution and assumed the centripetal force is equal to the centrifugal force, so that I could set the weight ...
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Beginner question: timelessness of massless particles [duplicate]

I am not very familiar with the quirkiness of relativity, and I was wondering how to explain this situation. If a beam of light is shining at some object at some distance from the origin of the beam, ...
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What is the relative acceleration of a projectile fired at in a low gravity vacuum?

This question is to end an old argument. Given a (space) vehicle with an acceleration of X, and projectile with an acceleration of 2X (rocket, not bullet), what would the relative acceleration of the ...
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1answer
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How to determine satellite position in J2000 from latitude, longitude and distance from Earth?

Due to my task of writing orbit prediction routines I am trying to understand the reference frames better and how to use them ( particularly for Earth orbits ). I think I get the idea of what ECI ...
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The particle content of a given state

In Carroll's we read ...The Unruh effect teaches us the most important lesson of Quantum Field Theory (QFT) in curved spacetime, the idea that "vacuum" and "particles" are observer-dependent ...
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How to differentiate between rotating frame and linearly accelerating frame?

Two friends, $A$ and $B$ are part of an experiment. $A$ is placed in a closed box and made to accelerate in free space at an acceleration $g$. $B$ is also placed in a closed box, but is made to rotate ...
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Free vs bound vectors and torque

When considering basic Newtonian mechanics, we can treat vector as free and move their point of application at will. This is consistent with the affine nature of Euclidean space. However, when ...
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1answer
66 views

Special relativity: circumventing velocity-addition formula

Two spaceships approach an observer from an equal distance and from an opposite direction with an equal speed $v$ in the observer's intertial reference frame $O$. The speed of a spaceship in the ...
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Static Friction on a Circular Road [duplicate]

I was recently brushing up on my dynamics, when I saw the interpretation of how a car moves in a circular road. Apparently, the car can stay in a circle due to static friction acting inwards. But I ...
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How the Bloch sphere of a Hahn echo in NMR looks like? 90-t-90-t-echo

I have tried to find in the literature a proper nice and beautiful Bloch sphere to describe the trajectory of a nuclear spin, starting in z-axis, using a pulse sequence of an initial 90º pulse with ...
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Experimental Verification of No Special Frames of Reference

Certainly, there have been numerous tests of both Special Relativity and General Relativity. Given all the phenomena and behavior stipulated by Relativity, one could perhaps divide these phenomena ...
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52 views

Quantitative relation between two charges moving in parallel in two frames of reference

The relevant question is here. The accepted answer may have explained my question in a descriptive manner. However, I want to see how things are related quantitatively. Imagine we have two charges ...
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What is $c + (-c)$?

If object A is moving at velocity $v$ (normalized so that $c=1$) relative to a ground observer emits object B at velocity $w$ relative to A, the velocity of B relative to the ground observer is $$ v ...
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3answers
64 views

Is time not a universal parameter, really, in special relativity?

I want to check that I get it right. The way that I have it in my mind is that, in my frame of reference and from my point of view, SR associates only one time parameter for the whole space, and not ...
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4answers
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Why would the apple fall under the tree?

Here is an extremely naive question: Why would the apple fall under the tree? I am puzzled by this, because the conventional answer that the gravity between the apple and the earth pulling apple down ...
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What do you really see on a line of clocks as you pass by them at high speed?

According to my understanding of SR, if I travel at 0.8c relative to a line of clocks, I should see the clocks in front of me going 3 times faster than my own, and those behind me going 3 times slower ...
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What is the linear and rotational motions generated by a force not on the CG?

Given a force that is applied to a free body, not directly towards, or away from the centre of gravity, how would you calculate the amount of linear and rotational velocities generated, as the farther ...
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Time difference in clocks of an accelerated frame [closed]

If we have two inertial frames $S$ and $S'$ and $S'$ is moving to the right w.r.t. $S$ with a velocity $v$. Suddenly $S$ undergoes negative acceleration (no longer being inertial) and after some time ...
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2answers
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Is Moon really rotating about its axis?

Wikipedia says yes but on Newtonian arguments. From general relativistic point of view Moon is not rotating but moving along geodesic trajectory. And like parallel transport of a vector (pointing to ...
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1answer
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Physical laws in all inertial frames

Do there exist physical laws which do not take the same form in all inertial frames?
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3answers
143 views

How to understand the definition of vector and tensor?

Physics texts like to define vector as something that transform like a vector and tensor as something that transform like a tensor, which is different from the definition in math books. I am having ...
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1answer
46 views

What would happen to a rocket car in a torus-shaped spaceship that encompasses the earth?

Suppose we built a enormous torus shaped space station that encompasses and leaves about 330 kilometers between it and the earth. So it's radius is about 6,371 kilometers . Obviously, this structure ...
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1answer
64 views

Bug riding on a ball moving at almost the speed of light [closed]

A ball with a bug on it is thrown at almost the speed of light. The bug looks back and observes the thrower throwing the ball. In the context of special relativity, what is the weight and the height ...
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In terms of physics, does the phrase “time slows down” mean the same thing as “things happen more slowly?”

The common definition of "time" is a type of measurement, like size. But the sentence "size gets bigger" doesn't make any sense. Is "time slows down" an odd phrasing of "events occur more slowly" or ...