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 dentoe particular coordinates chosen on the spacetime manifold.

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How do I experience Earth's movement?

We are told that Earth is spinning on its axis at 1037 mph— something that we don't usually feel because of the environment that moves with us as well. Is there any experiment with which we can know ...
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52 views

How do I know which observer is running the time faster or slower

Ok, I'm not a physicist, so I don't know if my question is silly (probably yes), but there is something in special relativity that I can't understand and I would really like it to be clarified. If ...
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277 views

Why isn't a Photon justified in concluding that it is at rest and everything else is moving past it at c? [duplicate]

Why isn't a photon moving at c not justified in concluding that it is at rest and everything else is moving past it at c since relativity postulates that the laws of physics are invariant (i.e. ...
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51 views

Implication of Relativity [duplicate]

According to relativity, no useful matter can travel faster than light. Suppose that your are a light beam travelling. Now you have a parallel light beam travelling beside you. Suppose you look at the ...
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Potential circualrity in end behaviors of heat death from decay of n singularities [closed]

ok first stackPhysics post for me so forgive any faux pas. The n body problem is classic. Regarding its simulation upon a manifold over t it can be interesting, and even beautiful. Now I am hoping ...
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69 views

Acceleration in a non-inertial reference frame

I have a conceptual doubt on the relation about the acceleration in a non inertial system. To explain the doubt without misunderstanding, I'm going to write the text of an exercise: A platform ...
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1answer
28 views

Does matter stacks up as it approaches Black hole?

When something approaches Black hole it'll experience time dilation with respect to a frame away from the black hole. So to an observer away from the hole the object would seem to slow down until ...
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2answers
51 views

Intuitive explanation of rotational inertia with respect to angular momentum

I understand that there are proofs (e.g. proof, another proof) of why the angular momentum about two points for an object is the same. However, could someone give an intuitive explanation of why this ...
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Weightlessness in Satellites

The following is written in my textbook as the reason for weightlessness felt in satellites: The gravitational pull is counterbalanced by the centripetal force. This introduces two problems: ...
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86 views

Triplet paradox

The situation is: A stay at a station B,C board the same train that moving away from the station while the train moving away C start moving inside the train in the opposite direction as such A sees ...
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32 views

Forces acting on a jet pilot [closed]

I found the forces at A and C with no problem, when it came to the forces at B I found the normal force of the seat on the pilot but the forces in the tangential direction got me. The solutions ...
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Frames of reference, energy and different observations (non-relativistic)

I have had trouble reconciling the quadratic form of kinetic energy and reference frames traveling at different velocities for some times now. I'll give an example that confuses me for some ...
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How am I able to stand up and walk down the aisle of a flying passenger jet?

The energy of a moving object is $E = mv^2\;.$ That is it increases with velocity squared. I walk at say 3 miles per hour, or lets round that down to 1 meter per second for a slow walk. I weigh less ...
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What is the difference between accelerating and boosting?

My professor claimed in class that there was a difference between an acceleration and a boost. I don't really understand the distinction. If you want to go to a different inertial frame of reference, ...
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51 views

Inertial forces and centre of mass

Is inertial force always attached to the centre of mass of the object? Why? What rules cause this to happen? See the example below of the leaned bike in a corner. The force $m\frac{v^2}{r}$ ...
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Distinguishing real forces and fictitious/pseudo forces in Newtonian mechanics

In understanding the law of inertia I had to consider the motion of bodies screened from the so called "real forces". What characterises these real forces? What makes us call them real? Or what is ...
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Man walking on the rotating platform [closed]

The problem is: The solid cylindrical platform with mass $M$ and radius $R$ rotates with angular frequency $\omega$. On the edge of the platform there is a standing man with mass $m$. Then man ...
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34 views

Simple Rotating frame of reference

I have a car moving in straight line with certain time-varying acceleration and there is another car moving in a curvilinear way along some curved path with some time-varying acceleration. The ...
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Reference frame and conservation of energy

Say spaceship $\alpha$ burns a portion of its fuel to leave planet A and is cruising through space at 10 m/s relative to the surface from which it launched. Spaceship $\alpha$ is being observed by ...
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Objective velocity (Relativity theory) [closed]

Suppose that I have a velocity of (approximately) $c$. Then I decelerate with $c$ per hour for exactly one hour. Then I would know that I would be standing still in the end, because the decelleration ...
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Does the speed of light differ for two frames moving at different speeds relative to an non moving observer?

Wikipedia says that: The speed of light in a vacuum is the same for all observers regardless of the motion of the light source. How can this be true and and returning to my question, if there is ...
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1answer
30 views

Does Earth rotation effect planes? [duplicate]

What about the supposed aiming modifications when firing a weapon? According to my research, when firing a weapon you are supposed to aim a little to the right when firing northwards and to the left ...
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2answers
46 views

Motion of an object in rotating frame

Yesterday I was looking at an old sloan video that describes motion in inertial and non-inertial frame. An experiment was actually like this. Two persons are sitting on the opposite side of a table ...
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Why do we only feel the centrifugal force?

After spending some time researching about the centrifugal force, I now understand that it is needed in a non-inertial reference frame for Newton's Laws to hold true. However, I don't understand why ...
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Acceleration in Space

Lets assume a body with a certain mass is in a region of space that has zero $g$ (or pretty close to zero $g$). Would acceleration in a straight line produce $g$-forces? Would that mass acquire ...
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Angular momentum changes depending on orign

Consider the image below where we have two point masses $m_1$ and $m_2$ with different masses which are rotating around a fixed axis with angular velocity $\omega$. If the origin is placed on the axis ...
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96 views

What force does balance centripetal force if centrifugal force doesn't exist in reality?

Which force does balance centripetal force? For example if we are rotating a ball tied with a string then centripetal force is acting inwards. Then which force balances it. I thought it is the ...
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Is it always possible to determine whether or not one is accelerating?

Consider the following two situations: A: You wake up in an elevator that is in free fall in a gravitational field. B: You wake up in an elevator that is floating in a vacuum. Is it possible to ...
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Can you shine a laser on an object that has fallen into a black hole? [duplicate]

I've been having a small back and forth on another website about the nature of objects that fall into black holes. I know that they never reach the event horizon from the perspective of a distant ...
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How to find the angular acceleration (rotating reference frames)

If you chose the frame to rotate with $w_1$ instead of $w_2$, wouldn't the angular acceleration be $w_2 \times (w_1 + w_2)$? and it would have $+20 \jmath$ instead? Shouldn't the absolute ...
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Deflection of a freely falling object [duplicate]

why Coriolis force acts on a freely falling body on earth as it is not in contact of earth surface? if a body being in contact of earth surface will suffer Coriolis force for earth's rotation if an ...
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1answer
57 views

Deflection of a freely falling body

Why Coriolis force acts on a freely falling body on earth as it is not in contact of earth surface? if a body being in contact of earth surface will suffer Coriolis force for earth's rotation but in ...
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34 views

Explain the centrifugal acceleration using the acceleration composition law

It's been a while since my last contact with physics, and recently i've met a probably very simple problem for which I'm trying to find a very formal explanation. In a "uniform circular motion" where ...
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Where does $\tan 2a = \frac{B}{A - C}$ come from? [closed]

I was reading about elliptical polarisation and stumbled across an equation involving the rotation angle of the ellipse. It has the form $$\tan(2a) = \frac{B}{A - C}$$ where $B$, $A$ and $C$ are the ...
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Work done changes between reference frames?

(This is not homework; a friend shared with me this puzzler and neither of us can figure it out.) Suppose you are in a plane traveling at velocity $v_1$ relative to the ground. The flight attendent ...
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Age of universe?

Well relativity teaches us that time interval between two events is a frame dependent quantity, then how can we say that our universe is 13.8 billion years old? Should it not depend on who is asking ...
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Are there any universal forces which are cartesian in nature? [closed]

I was recently talking with someone about how I think the whole Cartesian xyz understanding of the universe evolved from animals thinking earth was flat. They could get along fine without having to ...
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How is angular momentum conserved

from a classical perspective, what is it about angular momentum fundamentally that means it has to be conserved? Surely if I have a rod about a fixed axis and a moving particle hits the end it will ...
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How would you prove/verify that the real forces are independent of frame of reference?

How would you prove/verify that the real forces are independent of frame of reference?
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How would you explain the weight of an object in a lift accelerating up with acceleration a?

Observer in the lift:- He is unaware of his acceleration. He applies Newton's second law and got N = Mg. After that he used spring balance and found that the wait of the object is M(g+a). So to ...
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Minkowski geometry definition

The general relativity is based on Minkowski geometry definition with its special properties. The general relativity cant be approved wihout Minkowski geometry definition. Why Minkowski geometry is ...
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35 views

Does Coriolis force effect a particle that has only a tangential velocity in a rotating frame?

Imagine a disc rotating at an angular velocity $\omega$, a particle on the disc which is attached to the disc so its also rotating at an angular velocity $\omega$. Now the particle has tangential ...
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Most stationary object in the universe

There is an object in the universe for which the Sun appears to be more stationary as it travels through the universe than a star on some other system. There is probably another object for which both ...
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1answer
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Special Relativity in water

If there are 2 observers in water moving relative to each other as well as to water, they measure different speeds of light. So does time dilation occur for them? (since Time dilation is based on ...
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1answer
63 views

Why do we need theorems like **Parallel Axis Theorem**

In rigid body pure rotation, quantities like $\omega, \tau, L, I, r_i$ (symbol with usual meaning) are axis dependent. Assume rigid body to be sphere rotating about the axis passing trough the center. ...
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Operational Definition of Reference Frame in General Relativity

Most treatments of GR begin with the assumption that spacetime is a pseudo-Riemannian manifold (or, sometimes, that it is a more general manifold). But this entails quite a few tacit assumptions about ...
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1answer
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Simple frame of reference problem (conservation of momentum?)

I'm having trouble wrapping my head around a particular concept. Suppose we have a machine that fires balls of speed $u$ at some mass rate $\sigma$ (of units $\frac{kg}{s}$) directly at a car of mass ...
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47 views

Angular momentum about a moving axis

How can we define angular momentum of a system about an axis that moves parallel to itself? For example Axis passing through CM that is perpendicular to plane of body. When we talk about ...
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work done in observer frame

I had a few questions. 1) Is work done independent of the refrance frame? 2) Suppose a cart-A with rough surface is accelerating with an acceleration a and another cart-B with acceleration b. Now to ...
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Who told us how to measure torque?

We all know that force and torque are physical quantities which we have defined according to our purpose of work. Now we are all aware that Newton's Second Law from his Laws of Motion states how to ...