# 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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### What is the work done by friction on a body from the perspective of different observers using the formula $-μmgl$?

Consider two observers moving with respect to each other at a speed $v$ along a straight line. They observe a block of mass $m$ moving a distance $l$ on a rough surface. The change in KE of the block ...
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### Konig's Theorems

In the proof of Konig's Theorems the following identity is used: $$\underline{v_i} = \underline{v_i'} + \underline{v_c}$$ which is the law of transformation of velocity when passing from the ...
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### Angular velocity along a fixed rotational axis in space

I've been having some trouble getting my head around angular velocity and it's tangential movement, From what I think I understand the angular velocity has always a direction which is perpendicular to ...
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### Can a center of mass frame be non-inertial?

If I have a system with particles moving with varying accelerations such that it's center of mass is moving with accelerations (there is a non-zero net force on the system (acting on one or all of the ...
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### Why do equation of motion fail to apply in non-inertial frame even after applying pseudo force?

I considered two cars of equal mass moving towards each other with speed 30m/s and 18 m/s respectively and when they are 100 meters apart they both start de accelerating at 6m/s² each. So if we ...
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### What does size of an inertial frame mean?

It is the equivalence principle that provides the bridge between the ideal $SR$ model and the real world. According to it, we can find at each event a set of local inertial frames (LIFS), which may be ...
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### Time differential between two signals sent at two different near-relativistic speeds

There is something I don't quite get about relativistic velocities, which I am hoping to clarify with this question. Suppose you have an emitter and receiver both located somewhere far away from one ...
1 vote
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### The chronology of taking approximation changes the answer?

The problem is to find the time it takes a particle dropped from a height $h_0$ above the surface of the earth to reach the surface (exactly, not approximately i.e. $g$-value is not constant, in the ...
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### For someone staying on Earth, what is the minimum possible time to send a spaceship to Alpha Centauri and have it back?

Suppose we want to send a spaceship to Alpha Centauri and calculate the minimum possible time it will take for us here on Earth to have the spaceship back. We are not interested in how fast the time ...
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### How can one calculate the torque around this point? [closed]

I'll link to one of my previous problems, since the setup is very much alike this one for the problem I'll be solving: What happens with the pendulum when we choose this angular velocity for a ...
1 vote
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### Are curvilinear coordinates inertial?

At 1:46:34 of this lecture by Frederic Schuller, Inertial coordinates are defined as ones which satisfy the following equation: I am confused by the above equation because it would imply any ...
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### Why the proper time of photon is zero? [duplicate]

I'm currently taking classes on General Relativity, and whilst working on Geodesis equation: Find out that for mass particle q is equivalent to proper time but in case of photon the proper time of ...
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### How could any frame of reference be inertial?

The image below shows that a bystander watching the merry-go-round is in an inertial frame of reference. However, to nitpick, wouldn't the observer still be accelerating because it's on Earth?
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### Does the speed of an object underwater change when viewed above?

Let's say a submarine is coming to surface with a velocity $v$ normal to the surface of water and let's say you are the admiral of the navy viewing the submarine from the top. The submarine is exactly ...