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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Confusion regarding centrifugal force

In this https://youtu.be/YCrFwQtW5o0 sir took a disk and demonstrated that the particles kept on it fly away due to centrifugal force. Now, suppose I take a ring in free space and a placed particle in ...
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Work=Force Displacement Displacement relative to what?

Ok, taking the equation W=FD. Say a 30N force is acting on a 10kg object over 10s, causing it to move 150 metres over a frictionless surface. The work done by this force will be 30(150)J. However, if ...
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Equation motion of a material point on parabola through $\vec{F}=m\,\vec{a}$ [closed]

Consider a material point of mass $m$ that moves on a parabolic bowl $y=k\,x^2$, with $k>0$. In the reference frame of point: I have the following motion equations: \begin{align} \begin{cases} N-...
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Inertial and non-inertial frames

Firstly, I want to say that I realise that there are a lot of questions on inertial and non-inertial frames of reference, but the question I had in mind, no one seemed to have asked. I've just started ...
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Do I have the correct idea of time dilation?

Suppose that I send my twin away from the earth at 87% the speed of light. From the time dilation equation, since the twin is moving, the time interval between any 2 events, as measured by me, would ...
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5answers
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Magnetic force between 2 moving charges

If 2 positive charges are moving in the same direction with a velocity v relative to the ground frame, will they experience a magnetic force? I’ve read several times that the velocity in the Lorentz ...
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Do pseudoforces arise due to inertia?

Wikipedia says The fictitious force is due to an object's inertia when the reference frame does not move inertially, and thus begins to accelerate relative to the free object. The fictitious force ...
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Is inertia still considered a mysterious force?

When I first saw, for example, weightless objects in a space capsule, I assumed that pushing them would require no effort because, of course, they did not weigh anything. On Earth, heavy objects are ...
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Foucault pendulum equations of motion

All the sources I see for the equations of motion for the Foucault pendulum start with the small angle approximation. Does anyone know a source or textbook that does the full derivation? ...
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Why is the frame attached on the Earth non-inertial in General Relativity? ( neglecting rotations etc..)

The EEP says that freely falling frames are inertial. But suppose the freely falling frame is at some spacetime point. At that point you can by a suitable coordinate transformation reduce the metric ...
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How to transform coordinates from heliocentric to a view from earth?

I'm trying to find and model the apparent motion of the retrograde motion of Mars as viewed on Earth, incorporating Lagrangian or Hamiltonian mechanics. For the lagrangian I have: $L = \frac{1}{2}m_{...
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How to transform velocity 4-vectors to Zero Momentum Frame

I have a particle $p$ with speed $u$ in lab frame approaching a stationary particle $q$. The $p^{\mu}$ and $q^{\mu}$ velocity 4-vectors are: $$p_{LAB}^{\mu}=\gamma_u(c, u, 0, 0)$$ $$q_{LAB}^{\mu}=(c, ...
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Why do the steel balls in a spinning curved stand climb up?

I made a classical experiment to demonstrate centrifugal force. The experimental setup is made to stand vertically and spun along the vertical axis. The balls that initially rest at the bottom, on ...
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1answer
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Foucault pendulum: diagnosing experimental systematics

I did the Foucault pendulum experiment today. I used a 45 pound weight hung on about 12 or 15 feet of inelastic cord. I understand that a great and highly precise experiment will show one full ...
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What is the name for the technique where you solve an elastic 1D collision by moving to the center of mass frame?

At high school I was taught a method to compute $1d$ elastic collisions by first moving to the center of mass (COM) frame in which the velocities simply interchanged their sign. I recall the technique ...
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Combined Center of gravity

If I have two masses connected together, it's pretty simple to calculate the CoG of the system. But if the two masses are connected with a hinge? My question arrives from the motorcycle world. I'm a ...
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Why can't we surpass the speed of light? [closed]

Can anyone provide me with a complete mathematical proof about why an observer frame cannot surpass the vacuum speed of light? I have looked for answers in Quora and FB groups but no one is really ...
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What is the (relativistic) coordinate transformation between non-inertial reference frames?

I find it best to start this question with a thought experiment. We have a rocket ship and Earth. For our purposes, Earth has no acceleration or velocity and begins at the origin. The rocket ship ...
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What if a particle is observed from its own frame?

What if the net force on some particle is zero and we choose that particle itself as the reference frame or a frame moving uniformly relative to the particle. Can we call that frame an inertial frame ...
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Can rotation be distinguished from frame-dragging?

I am trapped inside the usual elevator and experiencing a comfortable gravitational field of about 1 g. Or perhaps it's an acceleration of 1 g. I cannot tell which. However, I notice when I drop an ...
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How to choose a proper reference point to apply conservation of angular momentum?

I am having trouble in applying the conservation of angular momentum in the following problem. A uniform rod of mass M and length a lies on a smooth horizontal plane. A particle of mass m moving at a ...
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Does the magnitude of heat energy given or taken the same in any reference frame

So the question consists of two parts- The random motion of the particles is equivalent the amount of heat energy. The velocity of collective motion does not result in heat energy. For example take ...
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Equivalence Principle on Earth

I've read that, according to the Equivalence Principle, no experiment can distinguish between uniform acceleration and gravity. If one is in the classically-described elevator with a basin full of ...
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Conceptual difficulty in a rotational dynamics

It is noticed that when a disk or something of that sort is rotated really fast and a small bead is put on it that bead flies almost radially outwards. Here's my problem: If there were no friction ...
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Why does force along center of mass produce translation motion? [duplicate]

I am not sure if I am asking a very complicated question but I want to know exactly what is happening at the molecular level that exerting force along center of mass produces linear motion and not ...
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How to solve this problem while taking torques about the lower end of the ladder?

This is a problem from my introductory physics textbook: The ladder shown in the figure has negligible mass and rests on a frictionless floor. The crossbar connects the two legs of the ladder at the ...
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Rotational velocity of water in spinning bucket

I'm trying to solve for the shape of the free surface of an incompressible, perfect fluid in a bucket which is spinning with (uniform) angular velocity $\Omega$. I know the solution is a paraboloid, ...
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Does the Earth orbit an ellipse or the barycentre of the Solar system?

I'm taking physics lessons in university and my professor described the Earth's orbit as en ellipse, where one of the focal points is the Sun (1st Kepler's law). However, this doesn't make much sense ...
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What exactly is center of mass?

I though I understood this concept but the more I learn advanced topics like torque, momentum, work, the more I realize that I have fundamentally misunderstood it. My original, theoretical line of ...
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Explaining rotation without mathematics

I understand why an object rotates about its centre of mass from a mathematical perspective but I have been trying to think how we can explain this in terms of the bonds within the object. Feel free ...
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How is causality preserved between observers in a cosmological setting?

Suppose that 2 observers are sending light signals to each other.If each of them are stationary in relation to a nearby galaxy, but each of these are separated by so great distance, they will be ...
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Inconsistency Regarding Instantaneous Axis of Rotation

I came across the following question in one of my reference materials: Method 1: I found the radius of curvature of the trajectory (for options B, C and D) by using the equation a=v^2/r, and I got ...
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Rigid body rotation apparent energy paradox

I'm doing some calculations on the motion of a rigid body as part of a project, and (as a tangent) I've come across something that I can't quite explain. Case 1: If I apply a force $F$ though the ...
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Einstein's relativity and body clock [closed]

Today we know biological factors of aging like DNA methylation increases & chromosome telomere shortens, that is we have an intrinsic clock. But Einstein suggests time stops at light speed & ...
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If 2 spaceships left Earth for the galactic centre, travelling near the speed of light, but they left an hour apart, would they arrive an hour apart?

If a spaceship left Earth for the galactic center at 3pm one day, traveling at extremely close to the speed of light (say 99.9999999%), then a second spaceship left at 4pm, would they arrive an hour ...
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Center of mass of a rocket

Is it correct to say that the center of mass of any space rocket is stationary here on earth? roughly speaking, without external forces the motion of the center of mass is preserved, so since the ...
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Equivalence Principle and Inclined Plane

During a discussion with a friend on the equivalence principle, the point was made that it only applies to objects in free fall, and therefore wouldn't apply to objects on an inclined plane. In other ...
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A tilted disk rolling on the floor

First of all, an image to describe the situation we have: Background A uniform disc is rolling without slipping on a flat surface. The disc itself is also in circular motion about the point $O$. I ...
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An airplane circles earth Eastward at constant altitude. Is the kinematical time dilation asymmetrical?

In the Haefele and Keating (H&K) experiment the airplane clock is only compared when reunited with the atomic clock on the ground. It is known that the H&K experiment showed asymmetrical ...
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1answer
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Importance of center of mass for ceiling fan

I am learning about center of mass these days. While doing so, I encountered the equation $$\sum {F_{external}} = ma_{com}$$ Then, it was written that with the help of this equation, it can be clearly ...
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Coriolis force and liquid on a rotating space station?

On a rotating wheel space station crewed by humans with sea-level conditions (temperature above the freezing point), if liquid was spilled on the floor am I correct in understanding that the Coriolis ...
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Why a mode on Minkowsky SpaceTime becomes two modes on Rindler Spacetime

----I am a student on Quantum Computing--- For the whole undertanding of "Tetrapartite entanglement measures of GHZ state with uniform acceleration" by Qiang Dong. https://doi.org/10.1088/...
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Twin paradox reinterpretation [duplicate]

What if we modify the experiment such that both twins have a spaceship and they both do exactly the same thing on time they agreed up front? They accelerate for 1 day the opposite direction. Then they ...
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1answer
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Effect of motion on ball in a moving cart

I know that in case of cart moving with an acceleration we are supposed to apply the concept of pseudo acceleration to judge the motion of ball in frame of the cart. Now , consider the case where ...
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Would an astronaut in this spacecraft feel weightless?

A spacecraft is placed in orbit around Saturn so that it is Saturn-stationary (the Saturn equivalent of geostationary – the spacecraft is always over the same point on Saturn’s surface on the equator)....
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Why is Torque defined the way it is?

According to my professor, Torque is like the connection of force in the angular world. But, we know that most quantities such as angular acceleration, angular velocity, etc. are defined as something ...
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1answer
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Pendulum in a stopping train [closed]

Can a pendulum reach the vertical ($\theta = 180^°$) in a train that brakes hard? I think the answer is yes but I don't see how to show that. I used the frame of reference of the train but I found ...
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Why two transformations quite different

I am a coder working on something related to robotics recently. This post is to know something I am not sure about the derivation of direct cosine matrix. I have two reference materials on the hand ...
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Reflection of light from a moving mirror with Lorentz-transformation

The trajectory of a moving mirror at speed $v\geqslant 0$ is given as $$s(t) = s_0 + vt.$$ A plane-monochromatic wave emitted from $x=0$ at $t=0$ with frequency $f$, given by $$\mathcal{E}(x, t) = \...
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Is there a difference in terminology between velocity vs velocity of the center of mass?

I was wondering if there was a difference between velocity of the center of mass of an object vs finding the velocity of an object in general. The case I was looking at was in a ball rolling without ...

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