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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Rotational velocity necessary to make apparent weight equal to “real” weight?
I have been trying to find a solution to this, but I never reach same one that my professor provides. The problem is the following:
For an object of mass m standing still on the surface of the ...
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1answer
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Speed of light in vacuum in non-inertial frame [duplicate]
Does the speed of light remains $c$ also in non-inertial frames? Or it changes from frame to frame?
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Why haven't we yet tried accelerating a space station with people inside to a near light speed? [on hold]
Is that something we could do if we use ion or nuclear thrusters?
Wouldn't people in the station reach 0.99993 speed of light in just ...
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1answer
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Boost as a generator of constant acceleration
In Covariant Loop Quantum Gravity by Carlo Rovelli p204, Sec 10.4, there is a paragraph which states
..., a trajectory at constant acceleration is generated by the boost
generator $K_z$ in the ...
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1answer
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Would conservation of angular momentum make it difficult to fall sideways in an O'Neill space colony?
It's always bothered me that the O'Neill space wheel puts forth centrifugal force as a suitable replacement for gravity. However, it seems the effects of conservation of angular momentum would induce ...
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2answers
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Inertial frames as in Landau & Lifshhitz mechanics 1st chapter
If we see inertial frames from a basic point of view (precisely more basic axiom from which I can at least derive the law of free body as in landau mechanics first chapter) that inertial frames are ...
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2answers
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The Earth revolves around the Sun or the Sun revolves around the Earth
Well, in today's world we know that the earth resolves around the sun. But that is seen from frame of reference of sun or an observer stationary wrt sun.
From frame of reference of the earth, sun ...
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Coordinate transformation of basis vectors
The question
Let $e_a$ be the coordinate basis vectors in a manifold described by coordinate system $x^a$. The vector displacement between two nearby points is given by
\begin{equation}
ds=dx^ae_a=dx'...
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How slow can time get near a black hole?
The closer I get to a black hole, does time slow down proportionally?
Does time stop near the event horizon?
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1answer
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Calculating acceleration of end point of rod
Suppose I have a rod hinged at its end, of length $\ell$ free to rotate about an horizontal axis; initially in the horizontal position and I have to calculate the acceleration of its other end point. ...
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2answers
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Interpretation of finite proper time of fast-accelerating objects for infinite coordinate time
Say we have an object with velocity in earth's frame that accelerates quickly.
For example, suppose we have some object that accelerates very quickly, and has speed $v$ in earth's frame of the form
...
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6answers
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How exactly does artificial gravity work?
A spaceship which uses centripetal rotation to create artificial gravity.
Must it always be accelerating? (The rate of rotation for it to work?)
If no, and even if yes, if one were to place ...
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Definition of Newton's first law [duplicate]
I have always had a doubt in the definition of the Newton's first law. In general, it is stated in a form like:
An object at rest remains at rest, or if in motion, remains in motion at a constant ...
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1answer
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Centre of mass location
How and why is com affected when an EXTERNAL force is is applied ?
What forces do we consider internal ?
Please provide some visual examples
Like men walking on plank, wedge mass system.
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Spaceship artificial gravity synchronization
Probably you remember the scene from "2001, Space Odyssey", where a small shuttle flies to low Earth orbit to reach a giant, ring-shaped mothership that rotates to generate artificial gravity, while ...
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1answer
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Sense of Coriolis force and Tractive force
I was solving a problem in Mechanics of material point and a part required to calculate the coriolis and tractive forces. So in the solution of this problem I realized that my answer missed the fact ...
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Invariance of forces
In Newtonian mechanics, the inertial forces depend on the reference frame and the other forces are invariant. Are they still invariant when special or general relativistic effect are involved?
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1answer
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What is proper name for non-inertial forces in GR?
General relativity works in all reference frames, so inertial forces are real in it. And due to the equivalence principle, gravity should be also considered inertial. So what is a good term for the ...
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1answer
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Journey away and back at close to the speed of light $c$
If a person drives away from a clock tower at a speed close to
$c$ for one whole day, and then drives back to it at the same speed (for another day), what would he see during each of the journeys?
I ...
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Issue deriving observed period of a moving signal in different reference frames
Consider a receiver on Earth measuring radio waves from an incoming slow moving UFO.
Here is my attempt to find the period of the signal as measured by the earth observer.
T' is the period of the ...
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1answer
44 views
In the case of a ball swinging in circular motion on a rope, w/out gravity or air resistance, what is the force pulling outward on the rope? [duplicate]
I'm thinking it is either the tension due to the ball, or the ball's centrifugal force. But the thing is, are these two forces the same in the conditions I've set (no gravity, no air resistance)?
...
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1answer
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Parallel axis theorem of stick-ball configuration
I have a system with a rod of mass m and length 2a. Let the origin be in the middle of the rod at x = 0. (Therefore, each end is a distance a away.) A ball of mass m is attached to the far right end. ...
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Single number to quantify difference between two local reference frames?
I'm working with some satellite data that defines the spacecraft reference frame from two star cameras and two different measurements of orientation configuration of the cameras, and I'm trying to ...
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0answers
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How to properly align my relaxed molecule onto my gold electrode?
the question is described below since it can be considered a chemistry or physics question: How to translate from one plane to another? originally posted on mathematics SE
I am trying to get ...
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3answers
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Does general relativity reduce to special relativity for free falling objects?
The following was stated in a general relativity lecture series:
"Full space is needed in GR. Minkowski space is sufficient for SR. However, Minkowski space is sufficient to compute properties of free ...
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1answer
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I want to know how to solve the following question from ground frame [closed]
Particle slides down a smooth inclined plane of elevation theta, fixed in an elevator going up with an acceleration a. The base of the incline has a length L. Find the time taken by the particle to ...
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Why does the parallel axis theorem apply in this case?
Next, the wheel is flipped over, so the angular momentum of the wheel is now negative. Obviously, the person must start rotating counterclockwise to conserve angular momentum. Since the person is ...
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2answers
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Is the parallel axis theorem valid for non-rigid bodies?
For some context, consider an idealized situation with a person, rigidly attached to the shaft of a bicycle wheel that can spin. sitting on a chair that can rotate. All bearings are frictionless.
...
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2answers
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Is the concept “space” actually needed?
I started making my mind around space and time and recently came to a point where I wondered if the concept of "space" is actually needed to describe physical processes at all and not just some ...
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2answers
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Throwing/Dropping an Object
When we throw or drop an object while moving, do we impart it our acceleration or velocity or both?
Say i throw a ball at 5 m/s (relative to me) while at say, 30° to my direction of motion, then will ...
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1answer
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Time in Lorentz transformations
I have a question about the meaning of time in Lorentz transformations.
When we say that event A for S' occurs at t', I understand that this ct' is a distance, but I wonder exactly what does it ...
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2answers
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Off-axis torque
If one adds pure torque to a disc rotating about a fixed axis in such a way that the application of the torque is off the axis of rotation with the torque vector parallel to the axis of rotation, does ...
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0answers
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Different prediction about the motion of a charge as observed by two different observers?
Suppose a charge is at rest in the laboratory frame. Also say two observers in two vehicles A and B are approaching towards it. Let A is accelerating towards it and B is moving uniformly towards it. ...
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1answer
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What is the direction of rotation of sphere on plank if a force is applied on the plank?
Suppose a solid sphere is kept on a rough plank , and then a horizontal force F is applied on the plank. Then in which direction will the sphere start rolling , given that no slipping takes place , ...
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2answers
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Modern arguments against Geocentrism?
In ancient times, the arguments for geocentrism were primarily from observation. It looks like the heavens revolve around the Earth, so "heavens revolve around Earth" is a reasonable first model. ...
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1answer
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Why doesn't the coriolis force cancel out when a ball is thrown up?
The question is to calculate the lateral displacement of a ball due to the coriolis force once thrown up and allowed to come back down.
The initial equation to work with is $\ddot{x} = -2\omega \dot{...
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1answer
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Terminology: can I use the world “comoving” to describe a reference frame in which a certain object is at rest?
Here a question about terminology. Suppose I have a particle that is moving at velocity $\beta$ in the observer (or laboratory) frame. Now, is it appropriate / legitimate to describe the frame in ...
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2answers
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Linear and angular momentum
If I push on an object not through the center of mass, we say that the translational effect on the entire object is the same. In other words, we can turn that off-center force into a force through the ...
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1answer
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Length contraction of an accelerating rod
Let us assume a rod of length, $4l$, initially at rest. The coordinates are defined s.t - (assuming uniform density)
$$X_{back-end}(0) = -2l$$
$$X_{front-end}(0) = +2l$$
$$X_{mid-point}(0) = 0$$
...
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1answer
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Does moment of inertia only work for special cases?
I was looking into the moment of inertia expression for angular momentum. The angular momentum of a group of particles can be expressed as a linear transformation of the angular velocity vector. This ...
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1answer
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A pseudo force problem [closed]
I got the following question in an app, while I was preparing for the exams.
A wedge is placed on a smooth horizontal surface. Wedge contains a circular quadrant of radius 25 cm as shown. An insect ...
2
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1answer
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How do you solve the twins Paradox? [duplicate]
I'm a beginner physics student only studying elementary AP-level physics and calculus, so when I came across the conceptual basis of the twins paradox I was, of course curious. People often explain ...
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2answers
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Is there “artificial gravity” created by a reference frame on a spinning object? [closed]
Believing the answer is yes, how then is spacetime curved? Will the spacetime uncurve when rotation stops? According to special relativity you can only see things from one's own reference frame. I do ...
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6answers
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Acceleration in free fall [duplicate]
A body in free fall "feels" no gravitational force (equivalence). Why does it continue to accelerate.
Why is your program refusing my question?
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3answers
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Force due to motion around Sun [closed]
Think of one person on earth named A . Ignoring Earth for a second, I can imagine him moving around the Sun due to which he should always feel some acceleration towards Sun (Centripetal Force) say F1. ...
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0answers
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Reference Frame conceptual confusion
I am getting confused as to why a ball still feels gravity when inside a moving car. The point of a reference frame is to reinterpret all the forces acting on a particle in one frame only. Hence all ...
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2answers
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A fictitious force in an orbiting frame of reference that is not rotating
Say we have an inertial frame of reference where there's a motionless star at the center and a planet is in circular orbit around it. We further assume that the planet is not rotating in the inertial ...
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1answer
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Is space in a rotating frame flat?
Apparently in papers like "Space geometry of rotating platforms: an operational approach" https://arxiv.org/abs/gr-qc/0207104 (page 21) and https://www.amherst.edu/.../view/10267/original/reden05.pdf (...
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The chain rule and velocity transformation in relativity (2)
First of all, these answers (How to derive the law of velocity transformation using chain rule?, The chain rule and velocity transformation in relativity, and other from a quick search on this site.) ...
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Does the apple fall towards the earth or does the earth move up to the apple? [duplicate]
Does an apple fall towards the earth or does the earth move towards the earth?...but if this is true then in the opposite side of the world would have to move towards them as well.
