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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If the equivalence principle is true, and gravity causes time dilation, why doesn't acceleration also cause time dilation?

I'm sure I must have something very confused but I'm just reading through SE questions and articles and this seems to be a contradiction. Until recently I had no problem as I assumed that acceleration ...
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Change of reference frame in quantum mechanics

I am dealing with a problem of a 2 level system (an ion in my case) placed in a Penning trap. Basically the ion is moving inside the trap under the influence of the magnetic and electric field and I ...
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Why is angular momentum conserved in a central field?

I am trying to understand how a gyroscope works, which in the broad strokes is due to conservation of angular momentum. I understand the case when the angular momentum passes through the origin of ...
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What rotates a door, torque or force?

I am confused as to what causes a door to rotate. Assume I apply a force to the edge of the door, with the door initially at rest. Force is perpendicular to the door, so it would create a torque. But ...
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Does the physical unit determine the length of the unit vector?

A vector quantity, like position, can be expressed as (using one dimension for simplicity): $$\textbf{r}=(1\ \text{m})\hat{\textbf{i}}$$ What determines how "long" the unit vector $\hat{\...
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Fluid pressure horizontal acceleration

A L-shaped glass tube with some liquid is kept in a train, which is accelerating at "a". If the height of A is 12 cm from reference shown and height of C is 8 cm, then find "a"? ...
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Component of component of vectors

Let's take an example to make you understand my doubt... A force $\vec{F}$ is in +$\hat{y}$ axis. First, I take $\pm 45°$ component of it both the sides against $\hat{y}$ axis... And then again, I ...
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What's the definition of angular momentum on a two-body system?

If some body it's rotating about the origin $O$ with constant speed, we can define the angular momentum as $$\vec{L}=\vec{r}\times\vec{p}\implies\frac{d\vec{L}}{dt}=0$$ Being $\vec{r}$ the position ...
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How can we find such an angle possible for this Q?

Here, a Bob is hanging inside a block which is moving with acceleration $7.5m/s^2$. Then, it has been solved that if the block moves with this acceleration. The angle subtended by the Bob inside the ...
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Proof in the theory of relativity [closed]

If the speed of a particle is smaller than the light speed in one inertial frame of reference then it is smaller than the light speed in any other inertial frame. This is a question our lecturer has ...
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With no frame of reference, which one is moving?

I understand that, to person A standing on a railway platform, person B on the train travelling past would seems to be aging slower (if such a thing were perceptible) and to person B it would appear ...
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Motion of a rigid body on application of constant force perpendicular to a point which is not the center of mass?

Consider a rod which has a uniform mass distribution which is free to move in space. Now, it is known that if an impulse (perpendicular to rod) is applied which does not pass through the center of ...
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Is the earth's version of time dictated by the earth's speed? [closed]

Is time on earth, relative to everywhere else, dependent on the earth's speed? Earth rotates at a speed, it moves around the sun, the sun moves around the galaxy and the galaxy is also moving - is it ...
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Applying torque to rigid body on a fixed axel?

Suppose I have a torque $\tau \in \mathbb{R}^3$ on a rigid body, about its center of gravity, where the direction of $\tau$ is the axis of the torque and the magnitude of $\tau$ is the strength of the ...
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Will the plane of oscillation of a pendulum change if I rotate the suspension point

I'm having trouble understanding Foucault pendulum and from that I've extracted one of my doubt and here it goes: A pendulum on a fixed platform is shown Now if we rotate the platform as shown Will ...
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Proving Earth is rotating by a water bucket at North Pole

If we put a bucket of water on the North Pole and if the water goes to the sides won't that prove that the earth is rotating?
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Would Foucault's pendulum work on the moon?

I am taking a course in introductory general relativity and came up on this question, which a google search didn't answer. The rotation of the Earth can be measured using a Foucault pendulum. The moon ...
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Pseudo-forces in revolving frame in contrast with rotating ones

A person in a rotating coordinate system, to do Newtonian mechanics has to use pseudo forces such as Coriolis and centrifugal. We use such forces for rotating coordinate systems,ones that rotate ...
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${}$Reference frames [duplicate]

Most of the particles have different velocity in different reference of frames but why is speed of light the same in all refrence frames? After all light is made of a photon.
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If I'm moving with velocity $v$, on something that is accelerating perpendicular to $v$, do I feel or detect a “Coriolis force”?

Can I detect a coriolis force? Or does coriolis force only apply to rotating accelerations? Do I feel something analogous to a coriolis force? It seems I must. Because on a small patch of the planet ...
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Why does Coriolis point this way intuitively?

The Coriolis force points as is shown. I understand it mathematically. I want an intuitive picture how it's true Say I'm in the rotating frame of the earth and I look at the particle in the northern ...
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How do we distinguish between systems and bodies when dealing with forces and moments?

In my preperation for an exam I came across the following question: In this question I treated the hinged laders as one body and thereby resulted forces and took moments. However, this does not yield ...
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Reference frame of non-localized particles?

In physics, a frame of reference (or reference frame) consists of an abstract coordinate system and the set of physical reference points that uniquely fix (locate and orient) the coordinate system and ...
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Why only one pseudo force for a revolving frame?

Pg 348, Kleppner and Kolenkow. Earth in a free fall towards sun is shown. Authors write The earth accelerates toward the sun at rate $\mathrm{A}=\mathrm{G}_{0}$ ... The apparent force to an ...
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A thought experiment to prove that Newtonian gravity is incomplete [duplicate]

A particle is at rest in one frame having mass $m$. It'll attract another mass proportional to its mass ( newtons law) . We jump into another frame moving close to speed of light. In this frame it's ...
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Height Of Mercury In A Mercury Barometer In An Accelerating Frame

I am currently in high school and I came across a physics problem that asked to find whether the height of the mercury in a mercury barometer would change when it is kept in an elevator that ...
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Angular momentum about centre of mass is not always equal to $I_\text{com}\omega$, Right?

Angular momentum about a point on the rotational axis is equal to sum of angular momentum perpendicular to rotational axis and angular momentum parallel to rotational axis. The perpendicular component ...
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Do all forces of nature produce opposite force when they move?

I am not sure if I understand it right but as I see it any two moving charge particles must repel each other like they are not moving relative to observer that moving at the same speed as they moving, ...
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Why is there a downward apparent force on an object accelerating upwards in an elevator?

In an upward accelerating elevator with acceleration a, from the inertial reference frame, a normal force equal to N= m(a+g) will be acting on the object inside the elevator of mass m. Now, for normal ...
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Conceptual question about instantaneous centers

In the following six bar linkage instantaneous center 2,6 ($P_{2,6}$ on the diagram) and slider D have equal velocity. But instantaneous centers have zero velocity and the velocity of other points on ...
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Galilean invariance in Electromagnetism

Griffith's Introduction to Electrodynamics when introducing Faraday's Law, considers two scenarios: Moving loop on a magnetic field. Current flows due to the motional EMF. The same scenario but on ...
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Showing that relative motion is independent of center of mass motion?

I am trying to understand the concept behind separating the center of mass motion and the relative motion in the Schrödinger equation for the Hydrogen atom. The idea is that the Hamiltonian given by (...
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1answer
153 views

What is the physical interpretation of four-force in SR?

Four-force in SR is the ratio of the relativistic momentum to the proper time $\tau$, however, the three-force has a different definition so that the coordinate time of $t$ replaces the proper one. ...
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On the working of the centrifugal force

I get that centrifugal force is what appears to force you out of a circular motion if you don't have the centripetal force required to stay in it. For example, a stone being whirled around on a string ...
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Why “frame of reference” can apparently mean two different things?

(Originally posted here, but apparently it is suitable for physics SE) There are several things about frame of reference in physics which I know. We may work in $\mathbb R^3,$ but this set is ...
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Does the four-force, in some ways, invalidate the results of the three-force in SRT? [closed]

I have recently submitted an article to PNAS, however, the editor, oddly enough, claimed that he has issues with the traditional Lorentz transformation for force, he stated: The argument of this ...
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1answer
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Equivalence principle and rotating frames

I understand that an observer in an uniformly accelerating frame in "free space" cannot distinguish this condition from the presence of a gravitational field. Or, at least, this holds "...
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What distinguished physical and pseudo-forces?

Why are some forces are considered pseudo-forces while some are considered real or physical forces? The definition of pseudo-forces that I know of is that they exist in noninertial reference frames ...
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Acceleration of static tetrad reference frame

I am trying to understand the calculation for the acceleration which a stationary observer in the Schwarzschild metric should experience $\nabla_{\vec e_0}\vec e_0 = -\frac{M/r²}{\sqrt{1-2M/r}}\vec ...
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Meaning of local tetrad in Schwarzschild metric

I have some interpretation issues with local tetrads and would like to discuss it with the Schwarzschild metric as an example. The metric can be defined as the inner product of a tetrad, $g^{\mu\nu}= \...
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When does Coriolis and centrifugal force act?

Ok so here is the situation you are on a disc rotating with the same angular velocity at the center so you are in a rotating frame of reference. A block is placed. Case 1: The disc is frictionless. ...
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Rotation matrices and reference frames

Lets say I have 2 3x3 rotation matrices, we will call them A and B. I am told to find frame B relative to A. how would I go about doing this basic operation? would I do it similar to position (with ...
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Why the formula of kinetic energy assumes that the object has started from an initial velocity of zero?

According to my physics textbook, the formula of kinetic energy is: $$ W = \frac{1}{2}mv^2 $$ Where $m$ is is mass of the object and $v$ is the velocity of the object. The equation is calculated from ...
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How do I find the inertia tensor of a tilted rectangular prism?

Suppose you take a rectangular prism with: width: 10 height: 10 depth: 20 the 10x10 face is facing in $x$ direction and apply a yaw movement of $\theta$ degrees. How would you find the inertia ...
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1answer
55 views

How does the derivative of time with respect to proper time equals gamma?

So, I want to really get a deep understanding of everything that goes beneath special relativity. Since I teach myself with books, I have no teacher to ask to which makes things a bit harder most of ...
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How to tell who is experiencing time slower and who faster when travelling at different speed?

I am trying to understand time dilation w.r.t velocity. Its said that when a satellite travels around earth (at speed more than a synchronized clock on earth which is stationary w.r.t earth), it ...
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When do we only consider an object's rotational kinetic energy?

I would like to ask a question in regards to an object's translational and rotational kinetic energy. Up till now, my understanding was that whenever you have a rotating body, you must consider both ...
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Accelerating rigid stick

I have read that in relativity, an infinitely rigid stick cannot be accelerated. So, I wonder what rigidity a massless stick of the length 1 m should have so to resist acceleration like a body of the ...
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Does special relativity imply that I can reach a star 100 light years away in less than 100 years? [duplicate]

I am just starting familiarizing myself with special relativity, and want to understand if the following is a correct thought process: Consider a star that is 100 light years away from Earth, from my ...
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How can I convert coordinate accelerations to proper acceleration?

I need to calculate what an accelerometer would feel from the motions from a simulation. The simulation only gives position data in a global reference frame. How can I convert this global positioning ...

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