Questions tagged [inertial-frames]

A specific reference frame that describes its coordinates in a manner that does not depend on time and is isotropic.

Filter by
Sorted by
Tagged with
5
votes
3answers
195 views

Definition of Newton's first law [duplicate]

I have always had a doubt in the definition of the Newton's first law. In general, it is stated in a form like: An object at rest remains at rest, or if in motion, remains in motion at a constant ...
0
votes
1answer
55 views

Necessity to consider the square of Four Momentum

Why do we often need to consider the square of four momentum transfer $Q$ in scattering experiment or particle physics/cosmology instead of just the $Q$ itself?
1
vote
1answer
118 views

In what sense do photons exist?

In a photon's frame of reference travel is instantaneous, so presumably a photon cannot exist in its own frame of reference. I am not aware that a "beam" of photons interacts via gravity despite ...
8
votes
6answers
1k views

Lorentz invariance of Maxwell's equations in matter

I know that Maxwell's equations of electromagnetism are Lorentz invariant in a vacuum. But what about in a generalized medium, e.g. a metal, a rubber, a dielectric, a magnet? I have read it comes down ...
1
vote
2answers
151 views

Newton's First Law and things that are very old [closed]

Recently I've been revisiting physics text books, and books by Feynman, and others. A curious thought has arisen, while I was reading about Mach's principle, and it seems to gnaw on my mind. I hope ...
1
vote
6answers
233 views

Twin paradox - is acceleration relative? [duplicate]

The usual answer to the twin paradox is that the twin who undergoes acceleration is the one who finds the other has aged more, because the trajectory of the 'travelling twin' does not amount to a ...
0
votes
2answers
70 views

Isn't inertia experience by person in moving bus same as torque

When a bus moves suddenly, the person standing in it tilts backwards. This concept is explained using inertia(tendency of body to resist change in its state of motion) but when the bus moves suddenly, ...
0
votes
0answers
32 views

Invariance of forces

In Newtonian mechanics, the inertial forces depend on the reference frame and the other forces are invariant. Are they still invariant when special or general relativistic effect are involved?
0
votes
1answer
36 views

What is proper name for non-inertial forces in GR?

General relativity works in all reference frames, so inertial forces are real in it. And due to the equivalence principle, gravity should be also considered inertial. So what is a good term for the ...
0
votes
1answer
139 views

Why does time slow down ONLY for objects travelling at high speeds?

Today in physics class, we learned about the theory of relativity and how it relates to time dilation. We were given the example of two photon clocks- one stationary relative to the Earth, and the ...
0
votes
1answer
59 views

Speed of light as the maximum speed and movement course

Assuming we have 3 objects d,e,f moving on the same line while e is stationary, d is moving to the left at 'almost speed of light' and f is moving to the right at 'almost speed of light'. What is the ...
0
votes
1answer
22 views

Fundamental Principle of Dynamics and equations of geodesics with proper time

I just wanted to have a little precision. In the expression below translating the PFD (Fundamental Principle of Dynamics) in tensor calculus (or more precisely the inertial principle) : $$a^{\nu}=\...
0
votes
1answer
62 views

How do we know who is moving? [duplicate]

If I am in a free float environment and there is another object at rest relative to me, and then I start to accelerate towards this object, do I know I am the one who is moving, since I am the one who ...
1
vote
1answer
85 views

Questions about special relativity, index in the Lorentz matrix

I'm studying special relativity I have read this: We have $ x^u = (ct, x^1,x^2,x^3) $. If we apply Lorentz transformation we can write: $x'^u = \Lambda^{u}_{\hspace{0,2 cm}\nu} x^{\nu} $ $x'_u =...
1
vote
1answer
111 views

Intuitive explanation for the Lorentz transformation for time

I've recently started learning SR, and while the Lorentz transformation for space is pretty obvious, just the Galilean transformation combined with space contraction, I can't figure out the ...
1
vote
0answers
30 views

What can I put in $x$ of Lorentz transformation? [closed]

Can I put "x = ct" in the red x?
0
votes
2answers
231 views

A simple proof covariance of Maxwell equations

I read that Maxwell equations are covariant under Lorentz transformations, but I can't find a proof. Or at least a proof understandable by someone that doesn't know higher mathematics (please don't ...
0
votes
2answers
51 views

Throwing/Dropping an Object

When we throw or drop an object while moving, do we impart it our acceleration or velocity or both? Say i throw a ball at 5 m/s (relative to me) while at say, 30° to my direction of motion, then will ...
0
votes
0answers
57 views

Newton's second law in non inertial frames: why am I getting $r_x = 0$?

Consider the following system: and the following frame: A rotating frame $x^{\prime} y^{\prime} z^{\prime}$ whose origin coincides with the inertial frame $x y z$ and the $z^{\prime}$ and $z$ ...
-1
votes
1answer
74 views

Thought experiment: if an observer can travel at the speed of light [closed]

What would the observer see if he could travel at the speed of light and shot a photon beam at the same time?
0
votes
1answer
43 views

Speed of light dependent on source velocity in other medium [duplicate]

Does speed of light depends upon the velocity of source in a medium (like water) other than space? if yes, does the speed gets added up when the light source moves in direction of light?
0
votes
2answers
70 views

Spaceship A and Spaceship B move in opposite directions at half the speed of light, and A fires a laser at B, does the laser light reach Spaceship B? [closed]

This question has been bugging me for a week now! I believe it would, but logically, I feel like I'm missing something. Please give a full explanation.
0
votes
1answer
62 views

Why doesn't the coriolis force cancel out when a ball is thrown up?

The question is to calculate the lateral displacement of a ball due to the coriolis force once thrown up and allowed to come back down. The initial equation to work with is $\ddot{x} = -2\omega \dot{...
0
votes
1answer
37 views

Terminology: can I use the world “comoving” to describe a reference frame in which a certain object is at rest?

Here a question about terminology. Suppose I have a particle that is moving at velocity $\beta$ in the observer (or laboratory) frame. Now, is it appropriate / legitimate to describe the frame in ...
0
votes
2answers
55 views

Conservation of momentum in different reference frames

Does the total momentum of a system in a given inertial reference frame have the same numerical value in other inertial reference frames?
0
votes
1answer
59 views

Lorentz transformations: Distance vs “retarded distance”

Suppose I have a charge situated at rest in one inertial coordinate system. The field of that drops inversely with the square of the distance. If I perform a Lorentz boost where $$v^2« c^2$$ (not ...
1
vote
2answers
59 views

A fictitious force in an orbiting frame of reference that is not rotating

Say we have an inertial frame of reference where there's a motionless star at the center and a planet is in circular orbit around it. We further assume that the planet is not rotating in the inertial ...
0
votes
1answer
41 views

Centre of mass problem

I came across a problem where there was an ice and tray system. The system was placed in a gravity free hall. After the ice melted the shift in centre of mass was to be found. But the answer is 0. Is ...
0
votes
1answer
88 views

Is this a right approach to show that $\partial_{\mu} \phi \partial^{\mu} \phi $ is Lorentz Invariant?

When trying to convince myself that $\partial_{\mu} \phi \partial^{\mu} \phi $ is Lorentz Invariant, I stumbled upon this approach: The last equation should read - $\partial_{i} \phi \partial^{i} \...
1
vote
2answers
90 views

What exactly is the meaning of length contraction? [duplicate]

Let's say a train of length $L$ (wrt ground) is standing on rails which have markings for every femtometre (or even smaller units). Now if someone takes a photograph and measures the distance between ...
1
vote
1answer
25 views

When do we illustrate inertial forces on inertial frames of reference?

I came across two practice questions wherein an object was attached to an accelerating vehicle, yet only one of these cases required an inertial force to be illustrated on the object's free body ...
0
votes
1answer
64 views

Will tidal effect make physics laws different?

I was reading Wheeler & Taylor's Spacetime Physics. The authors mentioned about tidal effect, as well as all physics laws are same in free-float frame. I am left wondering if tidal effect will ...
0
votes
1answer
45 views

Rapidity in 4-vector Transformation

In Lorentz transformation we have a concept of rapidity as related to boost. Rapidity is defined as a hyperbolic angle α such that $$\tanh(α)=v/c .$$ This further defines a matrix for Lorentz ...
4
votes
2answers
171 views

Is this relativistic mass?

I have seen in a lot of places in here clearly stating that relativistic mass is outdated, that we can make do just fine with the concept of invariant mass,etc. But I've also seen people saying that a ...
4
votes
1answer
252 views

Special *set* of inertial frames in an EM field?

Just looking for confirmation of my understanding of the Wikipedia article on classification of electromagnetic fields: The article states that in the case where $E\cdot B = 0$ and $E^2-B^2 \not= 0$...
5
votes
2answers
88 views

Spacetime diagrams and their interpretation

Recently started an introductory course of relativity, and started learning about space time diagrams. I couldn’t figure out what are the uses of a spacetime diagram as an alternative to Lorentz ...
1
vote
2answers
155 views

Problem with speed of light

I constructed a thought experiment, can't figure the answer. Two long (say $1\ \rm{km}$ long) railway cars are on parallel east-west tracks in a zero gravity environment. Each car has a light source ...
1
vote
0answers
27 views

The Lagrangian and inertial reference frames [duplicate]

From my understanding, my instructor told me that in order to use the Lagrangian, defined as $$L \equiv T - V,$$ to find the equations of motion via the Euler-Lagrange equations, the generalized ...
0
votes
2answers
104 views

Lorentz transformation of a Weyl Spinor?

A left handed Weyl Spinor belongs to the $(\frac{1}{2},0)$ representation of the Lorentz group. So given the Spinor, the unitary representation of the Lorentz transformation should look like $\exp{iA\...
3
votes
0answers
54 views

In Einstein's 1905 paper on electrodynamics, what he meant by energy of electromotive force?

In his 1905 paper, Einstein says that when the magnet is in motion and conductor stationary, changing magnetic field in space develops electric field "of certain definite energy", and this starts ...
1
vote
1answer
49 views

What is the physical argument for $d(G)_s = d(G)_b + d(G)_{rot} \quad ?$

In the book of Goldstein, Classical Mechanics, at the end of the page 171, it is stated that A relation between the two differential changes in $G$ can be derived on the basis of physical ...
0
votes
3answers
77 views

Inertial frames?

This is from a book. A traing is moving on earth. A ball is sitting at rest (relative to the train) on the floor of the train which is moving at constant velocity relative to a tree. If the ...
0
votes
0answers
42 views

Velocity addition formula derived from velocity boosts

I understand the derivation for the equation the velocity in a boosted frame by taking the boosts of the differentials such that: $v'^{\mu}= \frac{dx'^{\mu}}{dt'} $ where $x^{\mu} = \Lambda^{\mu}_{\, \...
1
vote
3answers
39 views

Defining what it means for a reference frame to move with a velocity $\mathbf{u}$ with respect to another

In describing a Galilean transformation, for example, one might say that if a reference frame $S'$ is moving at a velocity $\mathbf{u}$ with respect to $S$, then an object traveling at a velocity $\...
0
votes
1answer
59 views

Does special relativity causes magnetism? [closed]

And if yes, according to amperes law when the magnetic force beetween two current-flowing conductors the force is in linear reverse connection beetween the distance and the force, but if magnetism is ...
2
votes
1answer
87 views

How do time-like separated points preserve temporal ordering under orthochronous Lorentz Transformations?

How do time-like separated points preserve temporal ordering under orthochronous Lorentz Transformations? This question has already been asked in this Phys.SE post but I want to derive this result in ...
0
votes
1answer
73 views

The ladder paradox - with equal lengths

Take the usual ladder paradox in special relativity, but this time the ladder and the barn have the same length, at rest. Since each one of them contracts when viewed in the rest frame of the other, I ...
1
vote
1answer
56 views

Picking the Right Reference Frame

A space vehicle travelling at $3860 \ \text {kmph}$ w.r.t Earth sends its exhausted rocket motor backward with a speed of $125 \ \text{kmph}$ w.r.t the command module. The mass of the rocket motor is $...
0
votes
1answer
49 views

How to determine particle energies in center of momentum frame?

I want to show for the following process that, except for the angle $\theta$, all momenta and energies are fixed by energy-momentum conservation. Namely: $$p_A=\frac{1}{2\sqrt{s}}(s+m^2_A-m^2_B\space,...
1
vote
1answer
92 views

What motivated Einstein's postulate on the speed of light? [closed]

I know that there are several experiments (conducted after Einstein's formulation of Special Relativity) that confirm to some extend Einstein's postulate that nothing can travel faster than light. But ...