# 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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### When to NOT use centre of mass?

In case of a rod hinged about one of its ends and rotating about it in a vertical plane under influence of gravity, we cannot conserve energy about centre of mass. My leading explanation was that when ...
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### Doubt in parallel axis theorem exercise

My teacher solved a parallel axis theorem in class and I don't understand one of the steps he did The exercise consists of a coin of mass $m$ and radius $r$ moving on circles inside of a cone, the ...
1 vote
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### Centre of masses of 2 bodies together

If there's a system made up of 2 regular bodies (say a pickaxe: a uniform rod and a circular arc attached at one end), is it right to say that the centre of mass of the total body is just the "...
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### Conceptual meaning of frame of reference for kinetic energy

what does the statement The speed, and thus the kinetic energy of a single object is frame-dependent (relative) even mean? does the impact of a collision of moving bodies and henceforth transfer of ...
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### What experiment should be conducted?

Im self studying physics and came to this question in my textbook: A passenger in a moving bus with no windows notices that a ball that had been at rest on the aisle suddenly start to move towards ...
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### Trajectories of Non-Uniform Accelerations in Special Relativity

We have the following relation between the spatial part of the coordinate acceleration $A$ in an inertial frame and the proper acceleration $a$ in the comoving frame (supposing $1+1$ dimensions for ...
1 vote
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### Coriolis force relation to wind velocity

I'm learning coriolis effect on Winds moving from equator towards North pole. This is for geography. Question: Why is coriolis force stronger for winds having larger speed(larger component of ...
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### Why does torque increase with radius or distance from the centre?

Why is it that making a perpendicular force farther away from the axis of rotation increases the rate of change of angular momentum (hence, torque)?
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### Relativistic particle inside a moving relativistic frame [closed]

Special Relativity problem: In the laboratory frame, a particle at rest starts moving with a speed $c/2$ from one corner of a square (see figure) and traverses the four sides of the square so that it ...
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### What does each observer see's the others time as running slower mean? [duplicate]

I want to know whether the time of the one who accelerated to attain the velocity has slower time if they have a way to compare each other's time while there is a relative velocity between them if ...
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### How is special relativity explained by general relativity?

To be more specific about this, I am under the below assumptions and then will explain my question further. Please let me know if any of the assumptions are incorrect. (1) Special relativity describes ...
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### IMU frame to body frame

I am thinking about this problem: My IMU is centered at point O, and my structural body is centered at point p. Points O and P are two points on a rigid body. Point P is always moving and its motion/...
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### Why it is stated, that there is no inertial frame of reference?

According, to definition, provided, as I understand by Newton, there are frame of reference, where all constantly moving bodies keep their velocity constant, untill the force is not applied to such ...
1 vote
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### Question about distribution of mass

I recently began taking my first university-level physics course after having studied quite a bit of pure mathematics. While I think that my math background has helped me grasp some concepts a bit ...
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### Connection between pseudometric and Einstein elevator

I have a hard time understanding GR. I understand a lot (from a math point) about (pseudo)Riemannian manifolds, and I also learned about Einstein's elevator thought experiment. So let me elaborate: ...
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### Why does the work done depend on the frame of reference? [duplicate]

If I pushes a box due east for 1m by a 10 newtons of force, the work I do is 1J. But, if I consider the Earth's own rotation, the box actually has moved about 1km, and the work becomes more than 1000J....
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### Are the mass, diameter and age of the Universe frame dependent?

Mass of the observable Universe is known to be $1.50×10^{53}$ kg. Age is approximately known to be 13.7 billion years.The observable Universe is a sphere with diameter of roughly $8.8\times10^{26}$ m. ...
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### Time Dilation According to Stationary Object [duplicate]

Hello I am learning time dilation and I'm getting confused with some concepts: Consider the given scenario, in the frame of reference of the Earth an event takes 2 seconds to occur. In the frame of ...
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### Body on a frictionless rotatating surface [closed]

When we put a body on a frictionless rotatating surface. This body will be at rest relative to the non-rotating frame and analysing the body from lab frame we say $F=0, a=0$ but from the rotating ...
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### Teacher told us we're not allowed to write negative vectors, is this correct or not?

The question is a bit vague, so I apologize for that. To properly explain what I mean, I'll use an example. Let's say we've got two forces going left and right. $F_1$ is $20 \, \text{N}$, and will be ...
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### Rotating of a system of mass [closed]

In basic physics lectures, the teacher or professor in my class never explains the behavior of rotating two or many body particles. In my experience and intuition doing physics, two-particle or many-...
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### Choice of origin and change in angular momentum

I am now stuck on the impacts of choice of the coordinate system on the change in angular momentum and I would really appreciate it if someone can give me some help on this. Consider the following ...
1 vote
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### Equivalence principle and gravitons

If gravitons exist, are they always detectible in any frame? I'm asking because if I'm in a freely falling frame in a uniform gravitational field, and I detect gravitons, I will no longer be able to ...
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### Doubts about the parallel-axis theorem

I was studying about the parallel-axis theorem but had trouble making intuitive sense looking at it's derivation and statement. My confusion is that how is the moment of inertia about the center of ...
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### Is the size/age of the universe dependent on your velocity? [duplicate]

As Photons do not experience time or space, then according to my thought experiment, all photons must occupy some kind of singularity as well as what WE observe from earth. I was also thinking that ...
1 vote
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### Vanishing of angular momentum with scale

Most objects in the universe cycle around their centre of mass: earth, sun, galaxies. Even galaxy clusters. However, the whole universe doesn't possess an angular momentum. It can't: If it had one, ...
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### Can non-inertial/fictitious forces be understood as covariant derivatives?

From classical mechanics and general relativity, we know that the natural motion of a particle in general curvilinear coordinates, assuming the Levi-Civita connection, is given by the geodesic ...
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### Conditions Proper Frame

Suppose that we have an arbitrary trajectory in Minkowski space given by $$t = p(\tau) \quad \text{and} \quad z = q(\tau)\,.$$ I would like to find a transformation that brings me to the proper (...
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### How does the definition of a rigid body imply constant distance from the center of mass?

Let there be a system of N point-particles in 3D space, this system is a rigid body. The general definition of a rigid body is $\mid r_{i}-r_{j} \mid$=constant $\forall i,j$ In one of the books I was ...
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### Is the movement of earth absolute or does it just depend on the frame of reference

My understanding is that without acceleration the "movement" of a body is a relative concept, i.e. we can choose an inertial frame of reference where the body is at rest and there is no ...
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### Cause-effect definition of fictitious forces

I'm currently teaching a general-physics-for-engineers class, and we approached fictitious forces. As I was explaining them, students asked me how to discriminate "real" forces from ...
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### What force push ball outward in rotating tube in inertial frame? [duplicate]

Ball is free to move in hollow tube, if you rotate tube ball will move outward. What force push ball outward in inertial frame and how ball trajectory looks? (I know that centrifugal force don't exist ...
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### What will I feel if I experience a force in an accelerating frame of reference?

If I am in an inertial frame of reference, and I experience a force, what will happen is that I will accelerate relative to this inertial frame of reference. Say I am 60 kg and the force is 5 N and ...
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### Zero acceleration in circular motion while the body is accelerating

I was going through László Holics book (300 Creative Problems in Physics) and came across this question: The radius of the tire of a car is $R$. The valve cap is at a distance $r$ from the axis of ...
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### Misconception About Torque Log cutting example

LOG CUTTING "Three friends go camping in the forest with their families. They start collecting wood to make a fire. They find a large, branchless log in the forest. One end of the log is very ...
1 vote
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### Strange center of mass equation in AP Physics C

My post is an elaboration of those here and here. In my AP Physics C class, I was introduced to the following equation for center of mass (CM): $$x_\text{cm} = \frac 1M \int x\, dm.$$ Above, $dm$ ...
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### Proof angular velocity is invariant to translation on rigid body [duplicate]

My understanding is for a rigid body the angular velocity between two points fixed on the body is the same for all points. In other words the angular velocity vector would be the same. I can't find a ...
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### Is it possible to shift frame of reference to an electron?

We can see the world from different perspectives, from inertial frames to non-inertial frames. All that works very well but suppose I want to see the world from electron’s perspective then would I be ...
1 vote
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### Analytic description of oscillations in a rotating frame of reference?

Imagine you have a pendulum attached to a rotating axis. You define two frames of reference. In the $S$ frame, the pendulum is oscilating and rotating around this axis. The $S'$ frame is define such ...
1 vote
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### Magnitude Proper Accelaration Changes Under Coordinate Transformation

Rindler transformation are studied in the book of Carroll in Section 9.5. He starts from the Minkowski metric and a trajectory with uniform acceleration given by \begin{equation} \begin{split} t(\...
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### If you are in a frame which is fixed to the Earth's center, but not rotating with the Earth, is it inertial? [duplicate]

We usually treat the earth frame as approximately inertial. When we want to apply corrections, we use the centrifugal, coriolis and azimuthal forces. Are they all the corrections we would ever need? ...
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### How can Newton's laws of motion be true on the Earth?

The Earth, effectively a non-inertial frame of reference, is where Newton concluded his laws of motion. However, Newton's first law only holds in an inertial frame of reference. In the process of ...
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Imagine two reference frames that share same origin. One is static (S frame) and the other one is rotating (S' frame) with $\mathbf \Omega = \Omega_0 \mathbf k$. Imagine we throw a ball in an straigth ...