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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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Inertial and non-inertial reference frames

My book states that: A reference frame attached to earth is not inertial because it is revolving around the sun and it is rotating about its own axis. Don't we need a specified observer's frame ...
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What is my speed with respect to myself? [on hold]

Is it that my speed with respect me is always zero which means that throughout my whole life I am always at rest and the whole world is moving around me? I have another question: Suppose I am ...
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Velocity of a satellite with a polar orbit with respect to the surface of the earth

Let's say I'm tryng to derive the expression for the velocity of a really low orbit satellite. Let $S$ be the frame of reference of the earth's center (in rest). Let $S'$ be the frame of an observer ...
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How do I draw a diagram of the forces that create the “barndoor effect” (unbalanced torque) in rock climbing?

I have been asked to use a diagram that illustrates when a flag in rock climbing is necessary. I have no idea how to draw the forces involved in torque.
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Is a reference frame fixed (without rotation) on a precessing gyroscope an inertial frame of reference?

Let's say we put a human in a closed chamber which is going around a certain point at distance d from its center of mass at some angular velocity w. The centrifugal force on a human will be w squared ...
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Azimuthal Symmetry is on a certain axes that is not simply the $z$-axes

let's say in a problem, the azimuthal symmetry is along the axis $\frac{1}{\sqrt6}(-1, -1, 2)$. If I create two new basis angles and get solved the LaPlace's equation with that, what should I do to ...
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Total Pressure in a Non-Inertial Frame

After reviewing formulations for total pressure at low mach numbers, I concluded for a local reference frame that can rotate and accelerate relative to a fixed frame the total pressure for a fluid ...
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How to place the axis so that I can calculate the center of mass for the two instances?

I've got this: A wagon of mass $M$, initially at rest, can move horizontally along a frictionless track. When $t = 0$, a force $F$ is applied to the cart. During the acceleration of M by the force $F$...
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Transform an Inertia Tensor

I am trying to provide colleagues with a spreadsheet method of transforming the inertia properties of a complex shaped body to a different coordinate system, involving only rotation. I've read that ...
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Is a reference frame fixed (without rotation) on an axis of a precessing gyroscope an inertial reference frame? [duplicate]

Say a gyroscope is precessing about an axis parallel to a uniform gravitational field and the reference frame is precessing with the gyroscope but is not rotating around the gyroscopes axis of ...
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Would you feel inertial forces if you were inside a precessing gyroscope?

If a gyroscope is placed orthogonality on an physical axis which is paralel to a gravitational field if you're in a reference frame of the gyroscope do you have to modify Newton's law?
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Time derivative in rotating frame

In Goldstein (2ed) sec 4.9 - Rate of change of a vector, why does he say that the instantaneous angular velocity $\omega$ is not a derivative of any vector? $$ (d\textbf{G})_{space} = (d\textbf{G}...
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What is meant by 'The components of a force along a given axis'

I'm new to mechanics, and I'm having trouble interpreting what this means. So there's a force, okay. Then it has its components on the xyz axis, okay. But what does it mean by along a given axis, I ...
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Streamlines equation in a fixed frame

In this wikipedia article about potential flow around circular cylinder, the stream function is given by: $$\psi =U\left(r-{\frac {R^{2}}{r}}\right)\sin \theta \tag{1}$$ But in another article we ...
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Coordinate transformations in general relativity

Let's assume a non-rotating point mass with mass $M$. A non-massive object travels with constant velocity $\mathbf{v}_t$, with respect to the point mass, in the vicinity of the point mass. A non-...
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Would a human age faster if these certain conditions are met?

So, a human would travel in a rocket in outer space. There is little to no gravity, and the pressure may or may not have an affect (?) on what i'm about to ask. It has been proven that when a human ...
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Is MTW's argument in favor of Mach's principle valid?

Looking at older books, I was surprised to see that the general relativity "bible" by Misner, Thorne, and Wheeler is very strongly in favor of Mach's principle, which is treated in section 21.12. ...
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How can we use Newtons 1st and 2nd Laws on Earth when gravity makes all frames non-inertial?

As Newtons laws of motion only hold in inertial reference frames, how come we use them freely to describe motion of particles under the influence of gravity? Isn't the only frame where we can apply ...
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In which direction does the pseudo force act?

The point O is where the small mass is attached. I'm trying to find out the minimum velocity that should be given to the mass so that it can complete a full circle but if the fixed point is ...
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Proving the linearity of the transformations between inertial frames without assuming differentiability

All the references that I could find on the proof of the linearity of the transformations assume that the map that connects the coordinates between two inertial frames is at least once differentiable. ...
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What does the notation of the subscript behind the brackets in the differential mean?

From "Theoretical Mechanics of Particles and Continua" by A. Fetter and J. Walecka. As emphasized in the preceding section, the general expression $(7.11)$ can be applied to the coordinate vector $\...
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Can i use gravity to represent gravitational force?

Deduction for gravity: (in both deduction, m is consider to be a point mass) deduction 1: On the surface of the earth, gravitational force FG can be separate to two force component : mg(gravity) and ...
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Is it true that when you accelerate due to a non-gravitational interaction gravity is pulling you in the direction opposite to the acceleration?

We don't feel acceleration when we are only in a gravitational field due to equivalence principle as I understand it says gravity is simply inertia in spacetime. Is there any other type of force ...
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Does the Universe itself move to any direction on top of expansion?

So the universe expands right, but does this expansion move to any direction in hyperspace as an expanding cluster of matter somewhere? It's like if you would explode a bucket of paint under the. ...
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Finding instantaneous rotation and translation from multiple forces [duplicate]

I'm having trouble extrapolating torque, rotation, and such into the information I want. I'm trying to set up an estimation of a sea ship's movement for a game. The system is 2D. The ship has ...
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Centripetal acceleration of Centre of mass of rolling body

Does the centre of mass of body rolling on a stationary floor experience centripetal acceleration downwards towards the IAOR (instantaneous axis of rotation) which here is the point of contact of body ...
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Centripetal force on COM of rolling body? [duplicate]

Does the centre of mass of body rolling on a stationary floor experience centripetal acceleration downwards towards the IAOR (instantaneous axis of rotation) which here is the point of contact of body ...
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Confusion relating to setting reference point to $r=\infty$

Consider the diagram given below. If I put my reference point at infinity, then I get different line integral values for paths in blue and red, and hence different values and yet the integral $E.dl$ ...
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Since the Q-criterion is a scalar, does it not change upon moving reference frames?

Based on the definition from An objective definition of a vortex, the $Q$-criterion is $$Q=\frac{1}{2}(|\boldsymbol{\Omega}|^2-|\mathbf{S}|^2)$$ where $\boldsymbol{\Omega}$ is the rotation rate tensor,...
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Reference Frames and the De Broglie Wavelength

If the de Broglie wavelength of a massive particle, is h/mv then doesn't that mean interference patterns and everything change their properties depending on the velocity of the observer? How can QM ...
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Euler's equation of the rigid body's dynamics - Vector form with rigid body's angular acceleration

I have the following Euler's equations (9.23) ($\omega $ is the rigid body's angular velocity, $\Omega$ is the angular velocity of the reference frame whose origin is fixed on the rigid body and whose ...
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How are the predictions of the Schwarzschild solution consistent with our observations of black holes? [duplicate]

I am fully aware that there may be many misunderstandings in the following. However, in recent lectures we covered the Schwarzschild solution, and after some interesting mathematics we reached ...
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Direction of friction in non-inertial reference frame? [closed]

A beetle is moving radially with velocity $\bf{v}$ on a disk rotating with angular velocity $\bf{w}$. The coefficient of friction between the beetle and the disk is $\mu$. Find the distance $x_0$ ...
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Equivalence Principle and bending of light

Basically, the equivalence principle (EP) states that if someone is in a rocket in empty space with acceleration $g$ equal to that at the surface of the earth, any experiment he does cannot ...
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Human Body Upward Acceleration on Scale [closed]

I am reviewing for a Physics exam, and have come across the following example question: If I weigh 200 pounds, but a scale I'm standing on reads 400 pounds, then I am accelerating upward at 1g 2g 3g ...
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How do you sum up torques for a macroscopic object

Torque is measured about a point. But angular momentum for some object is measured around an axis. This doesn't make sense to me as in for example, a cylinder. If there are multiple tangent forces on ...
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Motion at absolute 0 in relative to [duplicate]

Hypothetically, if we could get some type of particle to be at absolute 0 would it be technically still have relative motion due to an observer outside of earth. E.g earth is moving therefor particle ...
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Is a *difference* of potential energy relative to a frame of reference?

If we consider an electrical field, or a gravitational field, and two points in this field, is the difference of potential between this two points depending of a frame of reference ? It seems to me ...
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Angular velocity of a body observed from a frame of reference fixed on the body

I have a body and the reference frames, one is the inertial reference frame O-xyz, the other is a non inertial reference frame O'-x'y'z' fixed on the body. The angular velocity vector of the body ...
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How do frames of reference work in general relativity, and are they described by coordinate systems?

In both Newtonian gravity and special relativity, every frame of reference can be described by a coordinate system covering all of time and space. How does this work in general relativity? When an ...
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Detecting external 'forces' in an inertial frame

Disclaimer: Science noob here, I may not use all terms correctly. I've read somewhere of the following situation: An observer is inside a room (elevator) with no ...
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Reference frames and Newton’s second law

I have an understanding Issue. We were told that apparent weightlessness was due to the absence of Normal Reaction force.The example chosen was a man in a lift...the latter moving with different ...
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Einstein's Elevator - Constant acceleration eventually reaches $c$. Can't that be used to detect gravity vs acceleration?

Objects with mass that continuously accelerate will eventually approach $c$, but cannot exceed it. So if I find myself in an elevator, unable to determine if I'm in a uniform gravitational field or ...
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Acceleration interpretation in accelerated frames in general relativity

I would like to know whether my physical interpretation of some dynamics in accelerated frames is correct. In a frame with acceleration $a$ we have the metric $$ds^2 = (1+ax)^2 dt^2 - dx^2$$ The ...
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A confusion between geocentric and heliocentric model [duplicate]

As per Ptolemy, he proposed firstly geocentric model and that model if one see with aspects of relativity he would find true. Here is an example how Suppose you are in a train which is moving and you ...
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Gravity on hovering objects

Imagine a remote controlled toy helicopter vertically takes off from a table and hovers at about one metre over the table that is of one metre height: hence, the total altitude is 2 metres. What will ...
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If there was but one object in the universe, can it be accelerating or not accelerating?

If there is only a single (material) object in the universe does it still make sense to speak of it as accelerating or not accelerating? I believe it might be an equivalent question to ask whether it ...
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Are Euclidean solutions also solutions of Einstein's equations?

In Special relativity we have the metric $(+---)$. But in General relativity we have a metric tensor $g$. In the equations themselves there doesn't appear to be anything that tells you what the ...
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How one can actually define an infinite family of Momentarily Comoving Reference Frames (MCRF)?

In Griffith's General Relativity there is the following line: An accelerated particle has no inertial frame in which it is always at rest. However, there is an inertial frame which momentarily has ...