The inertial-frames tag has no wiki summary.
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Proof that the Earth rotates?
What is the proof, without leaving the Earth, and involving only basic physics, that the earth rotates around its axis?
By basic physics I mean the physics that the early physicists must've used to ...
22
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8answers
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What is the Earth truly rotating about/revolving around?
Earth rotates on its axis and revolves around the sun, the sun revolves around the galaxy, the galaxy is also moving. So Earth's net rotation as observed from a fixed inertial frame consists of all ...
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4answers
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Newton's Bucket
Newton's Bucket
This thought experiment is originally due to Sir Isaac Newton. We have a sphere of water floating freely in an opaque box in intergalactic space, held together by surface tension and ...
12
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2answers
1k views
Deriving the Lagrangian for a free particle
I'm a newbie in physics. Sorry, if the following questions are dumb. I began reading "Mechanics" by Landau and Lifshitz recently and hit a few roadblocks right away.
Proving that a free particle ...
11
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8answers
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Is Mach's Principle Wrong?
This question was prompted by another question about a paper by Woodward (not mine). IMO Mach's principle
is very problematic (?wrong) thinking. Mach was obviously influenced by Leibniz. Empty space ...
10
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13answers
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What are the mechanics by which Time Dilation and Length Contraction occur?
What are the mechanics of time dilation and length contraction? Going beyond the mathematical equations involving light and the "speed limit of the universe", what is observed is merely a phenomenon ...
10
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4answers
356 views
The definition of an inertial reference frame in Einstein's relativity
I'm reading Sean Carroll's book on general relativity, and I have a question about the definition of an inertial reference frame. In the first chapter that's dedicated to special relativity, the ...
8
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6answers
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What determines which frames are inertial frames?
I understand that you can (in principle) measure whether "free particles" (no forces) experience accelerations in order to tell whether a frame is inertial. But fundamentally, what determines which ...
8
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4answers
884 views
What does a frame of reference mean in terms of manifolds?
Because of my mathematical background, I've been finding it hard to relate the physics-talk I've been reading, with mathematical objects.
In (say special) relativity, we have a Lorentzian manifold, ...
8
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2answers
667 views
Does the speed of light vary in noninertial frames?
The speed of light is the same in all inertial frames.
Does it change from a non-inertial frame to another? Can it be zero?
If it is not constant in non-inertial frames, is it still bounded from ...
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11answers
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Why do we say that the earth moves around the sun?
In history we are taught that the Catholic Church was wrong, because the Sun does not move around the Earth, instead the Earth moves around the Sun.
But then in physics we learn that movement is ...
4
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3answers
795 views
Is acceleration relative?
A while back in my Dynamics & Relativity lectures my lecturer mentioned that an object need not be accelerating relative to anything - he said it makes sense for an object to just be accelerating. ...
4
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4answers
127 views
When we talk about speeds in relativity theory, where are they measured?
I recently asked a question here about if the direction we travel matters in relativity theory:
Does it matter in which direction I travel in relativity theory?
After I got answers and making more ...
4
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2answers
252 views
What is the formal definition of a stellar day?
I'm having trouble understanding precisely what a stellar day is. Neither the USNO nor the IERS sites provide a definition. And Wikipedia's description as the "rotation period relative to the fixed ...
4
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2answers
391 views
Can an “absolute” frame of reference be determined by measuring the compression of light?
General relativity tells us that there is no absolute frame of reference (actually, it tells us that all frames are relative, which is close but not the same as there is no absolute frame).
Special ...
4
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2answers
396 views
Landau's ambiguous statement about the existence of inertial frames
Landau writes "It is found, however, that a frame of reference can always be chosen in
which space is homogeneous and isotropic and time is homogeneous."
Does he mean that we can prove the existence ...
4
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1answer
257 views
Is momentum conservation for the classical Schrödinger equation due to non-relativistic or due to some more exotic invariance?
I had no problem appliying the Neothers theorem for translations to the non-relativistic Schrödinger equation
$\mathrm i\hbar\frac{\partial}{\partial t}\psi(\mathbf{r},t) \;=\; \left(- ...
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6answers
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Is there any true inertial reference frame in the universe?
Is there any true inertial reference frame in the universe?
Newton's first law states that an object at rest remains at rest, and an object performing uniform motion performs uniform motion, until ...
3
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1answer
294 views
The form of Lagrangian for a free particle
I've just registred here, and I'm very glad that finally I have found such a place for questions.
I have small question about Classical Mechanics, Lagrangian of a free particle. I just read Deriving ...
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2answers
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What is the inertial frame that explains the Foucault Pendulum?
I know that the Foucault pendulum rotation in relation to Earth is a proof that the object is inertial in relation to the distant stars. But what makes them more important than the Earth? Are they an ...
3
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5answers
165 views
Will a warm body naturally slowdown?
Suppose a warm body moving in an empty space with high speed.
The body emits radiation based on its temperature. The protons emitted forwards of the body will have higher energy due to Doppler shift ...
3
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2answers
209 views
Cosmic Microwave Background (CMB) and its relation to Inertial Frames
We know that the CMB is isotropic when viewed outside of the spinning and revolving earth.
Is it homogeneous?
Can we relate the CMB to an inertial frame in the Newtonian sense (in which space and ...
3
votes
4answers
434 views
How fictitious are fictitious forces?
How fictitious are fictitious forces?
More specifically, in a rotating reference frame i.e. on the surface of the earth does an object that is 'stationary' and in contract with the ground feel ...
3
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3answers
103 views
Newton's First Law of Motion; Empirical Aspects
Newton's first law states that in an inertial frame, a body at rest continues to be at rest, and a body in constant rectilinear motion continues its motion, unless an external force is applied upon ...
3
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2answers
177 views
Second law of Newton for variable mass systems
Frequently I see the expression
$$F = \frac{dp}{dt} = \frac{d}{dt}(mv) = \frac{dm}{dt}v + ma,$$
which can be applied to variable mass systems.
But I'm wondering if this derivation is correct, ...
3
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1answer
268 views
Problem with convergent geodesics at 2D sphere
There is a chapter on general relativity in the book Spacetime Physics Introduction To Special Relativity by Taylor and Wheeler, which qualitatively explains how attractive gravitational force can be ...
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3answers
310 views
The two faces of $F = m*a$
As I have understood,
$F(t)=m \cdot a(t)$
can have 2 different meanings:
When applying an external force $F$ on a point mass of mass $m$, the resulting acceleration of that mass at time $t$ is ...
2
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2answers
172 views
Fictitious forces confusion
I have a hard time understanding the subject of fictitious forces. Let's discuss a few examples:
1) I'm sitting inside a vehicle which is accelerating in a straight line. I feel like someone is ...
2
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2answers
175 views
Foucault pendulum
The equations of motions for a Foucault pendulum are given by:
$$\ddot{x} = 2\omega \sin\lambda \dot{y} - \frac{g}{L}x,$$
$$\ddot{y} = -2\omega \sin\lambda \dot{x} - \frac{g}{L}y.$$
What are the ...
2
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2answers
487 views
Galilean transformation in relativity
Assume flat spacetime in a general relativistic framework (or special relativity for that matter) and two observers $A$ and $B$, with non-vanishing velocity relative to each other. We know that they ...
2
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1answer
226 views
What happens to speed and frequency of a light beam moving in transparent medium when observed from different inertial frame of reference?
Suppose a transparent medium where speed of light is $c/n$, an inertial frame of reference $K$ which is stationary relatively to the medium and an inertial frame of reference $K'$ which is moving ...
2
votes
1answer
129 views
Galilean relativity in projectile motion
Consider a reference frame $S^'$ moving in the initial direction of motion of a projectile launched at time, $t=0$. In the frame $S$ the projectile motion is:
$$x=u(cos\theta)t$$
...
2
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1answer
147 views
Why can we use just one angular velocity vector to describe the rotation of a whole non-inertial reference frame?
The other day in class the professor was explaining non-inertial reference frames. We were working out how to find the acceleration of a point as measured from the non-inertial reference frame, and ...
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0answers
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does a rotating moving body in “flat” space curve its path because of frame dragging?
I am not a physicist.
let's say we have a space with an object in it, where all other gravitational bodies are so far away that their affect on the shape of the space is negligible.
let's say the ...
2
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2answers
81 views
Reality error and relative velocity
Suppose a person is walking in rain carrying an umbrella. He is tilting his umbrella at some angle with the vertical so as to protect himself from the rain. But a neutral observer who is standing ...
2
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2answers
520 views
Earth-Centered Inertial (ECI) reference frame as approximate inertial frame of reference
In many practical applications, one can consider the Earth-Centered Inertial (ECI) reference frame approximately as an inertial reference system, though strictly speaking, it is non-inertial.
Is ...
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2answers
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Fictitious Forces $\overset{?}{⇔}$ Constraint Forces (re: D'Alembert's Principle)
Are fictitious forces and constraint forces the same thing?
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2answers
247 views
Using Lorentz Invariance of Charge To Calculate Current Density
I'm attempting a problem from Zwiebach: A First Course in String Theory and am completely stuck. Could anyone give me a hint? The problem is as follows.
Consider $S$, $S'$ two Lorentz frames with ...
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4answers
244 views
Freefall in/out of an enclosed environment
I've just been learning about Einstein, relativity, and the equivalence principle in Physics. I'm fascinated with the idea of being inside a free-falling enclosed environment (such as, e.g., rocket, ...
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3answers
257 views
How to take into account the reference frames with the revolution and rotation of the Earth in OPERA's superluminal neutrinos?
Since the Earth is moving around the Sun, which is moving around Milky Way, etc... What reference frame is used for the complete motion of the begin/end points (which are non-inertial right?)?
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1answer
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Accelerating expansion of universe - entire universe a non-inertial frame of reference?
If the expansion of the universe is accelerating, doesn't that mean that the entire universe is a non-inertial frame of reference? And if so, what implications does this have (if any)?
1
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1answer
72 views
Is it best to look at light as a particle when trying to understand special relativity?
So my course about special relativity explains time dilation using a moving train, where one sends up (i.e. perpendicular to the direction of movement) a light pulse which gets reflected etc. (a ...
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2answers
564 views
Flying a toy helicopter inside an accelerating train
Scenario:
You ride in a train, you have this helicopter toy. The train is not yet running when you flew your helicopter on a constant altitude (say 1 meter above the train's floor).
Question:
What ...
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1answer
233 views
centrifugal force in static frame of reference
The other day we derived Kepler's third law.
$$
\left( \frac{T_1}{T_2} \right)^2 = \left( \frac{r_1}{r_2} \right) ^3
$$
In order to derive this, you can look at a given planet that revolves around ...
1
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1answer
125 views
equivalence principle and nontrivial compactifications
it is commonly argued that the equivalence principle implies that everything must fall locally in the same direction, because any local variation of accelerations in a small enough neighbourhood is ...
1
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1answer
104 views
The definition of Lorentz transformation
I know that the Lorentz transformation, when two frames $\mathcal{S}$ and $\mathcal{S}'$ are in standard configuration (the axes are all parallel to their counterparts in the other inertial frame) is ...
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1answer
77 views
A physical sense of an Inertial frame
Definition clarification needed, please: I am hoping to get physical sense of an "inertial frame".
Do inertial reference frames all have zero curvature for their spacetime?
So is an inertial frame ...
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4answers
754 views
Inertial frames of reference
I'm struggling with the notion of an inertial frame of reference. I suspect my difficulty lies with the difference between Newtonian and relativistic inertial frames, but I can't see it.
I've read ...
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2answers
970 views
Argument for proving Earth-Centered Earth-Fixed (ECEF) reference frame is non-inertial
Today I heard an argument to prove that the Earth-Centered Earth-Fixed (ECEF) reference frame is non-inertial. It seriously doesn't make any sense to me but I also heard that same argument was made by ...
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3answers
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Centripetal/Gravitational Force
Suppose a satellite is orbiting the Earth. The gravitational and centripetal force supposedly point towards the Earth. Therefore, the net force is towards the Earth. Since the satellite doesn't fall ...
