# Tag Info

## New answers tagged reference-frames

5 votes
Accepted

### Time differential between two signals sent at two different near-relativistic speeds

This is a very interesting question. Indeed, as a one-way-speed-of-light (OWSOL) experiment the answer is a duplicate of all of the other myriad OWSOL questions: there is no possible experiment which ...
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### Why do equation of motion fail to apply in non-inertial frame even after applying pseudo force?

Your computation in the inertial frame seems to be correct. However, car 2's deceleration in car 1's frame is wrong. Let's look at this in detail. Let $D$ be the distance between the car when they ...
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2 votes
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### What does size of an inertial frame mean?

The Equivalence Principle (EP) is valid locally: if you perform a local experiment in an inertial frame of reference, you can't say if you're freefalling or not falling, you can't say if you're ...
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### What does size of an inertial frame mean?

I've never seen it phrased like that, but I understand it as the following. Strictly speaking, the frame is defined locally, on a point. So the further you move from that point, the less inertial the ...
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1 vote

### What does size of an inertial frame mean?

I don't have the book but I think he means the following. At any point in spacetime you can assign an inertial frame, similar to how you can assign a tangent line to a point on a curve. The size of ...
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### The chronology of taking approximation changes the answer?

I've found out where the error was, it was not due to chronology of taking approximations, instead I had done error while approximating $\arctan(\sqrt{\frac{h_0}{R}})$. Let $x=\frac{h_0}{R}<<1$, ...
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-2 votes

### Time differential between two signals sent at two different near-relativistic speeds

Photons are bound by relativity. Even if a really fast vessel. It is o ly when an object approaches 1/10th c that dilation becomes heavily noticeable. One aspect of Special Relativity speed of light ...
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1 vote
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### How can one calculate the torque around this point?

The short answer What you did wrong, is you forgot to the contribution of momentum to angular momentum. $$\vec{L}_P = \vec{L}_{\rm COM} + \vec{r}_{\rm COM} \times \vec{p}$$ The second thing wrong is ...
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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?

The minimum time, as measured on Earth, for anything to travel to Alpha Centauri and back is 8.74 years or thereabouts, if the something was massless. For something massive like a spaceship the time ...
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2 votes
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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?

As the spaceship accelarates, at which point the time dilation added due to the incrase of speed starts to increase the total time of the journey measured on Earth? Never. If the ship can accelerate,...
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2 votes
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### Are curvilinear coordinates inertial?

Indeed, it is valid to consider that polar coordinates are non-inertial. You should be aware that the term “reference frame” does not have one unique meaning. Different authors may use it to mean ...
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### Are curvilinear coordinates inertial?

Reference frames can be inertial or non inertial. Coodinate systems are not reference frames unless the frame is somehow being tied to the coordinate system. Does the book explain how the frame is ...
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### Why the proper time of photon is zero?

Because for a massless particle $ds^2=0$.
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9 votes
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### How could any frame of reference be inertial?

In newtonian mechanics, inertial frames are an equivalence class. They can be defined as frames where Newton's laws are valid. If you can find one inertial frame, then you automatically get an ...
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### A question about relativity and time dilation from a lay-person

The best way to see what's going on is with a special Minkowski Diagram called a Lodel Diagram. Let's say the unprimed frame is on Earth, and the primed frame is the returning rocket ship. Since you ...
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### A question about relativity and time dilation from a lay-person

Time dilation can be confusing until you view it in the right way, and then it becomes obvious. Time dilation is caused because clocks in two moving frames are out of synch relative to each other- it ...
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### A question about relativity and time dilation from a lay-person

Alice is on earth. Bob travels from Far Away. The story according to Alice: At 2PM, Bob started his journey, with his clock correctly set to 2PM (as was mine). The journey took him four hours, but ...
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### A question about relativity and time dilation from a lay-person

When you say "he will reach the Earth in one week" you have to also specify whether this is as measured by A or as measured by B. They have different coordinate systems. They're both ...
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### A question about relativity and time dilation from a lay-person

It is better to think of a row of ships travelling to earth with the same velocity of A (Alice) and with synchronized clocks. And a row of stationary clocks synchronized with the B (Bob) earth's clock....
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1 vote
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### Would an accelerated-time space region deflect projectiles?

Time runs slower in a gravitational well than far above. From this, Einstein derived that light is deflected when it passes near the Sun. He predicted that a star whose apparent position is very near ...
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4 votes
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### Dependence (or lack thereof) of forces on frames of reference

When you say "blocks A and B move with a relative acceleration of -3 m/s2" you are considering the motion of one block in the reference frame attached to the other block (block C). But the ...
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1 vote
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### Galilean Transformations Derivation

Let's analyze the spacetime coordinate from the Greek perspective. The Greek will see that the Roman will approach him/her an meet at origin coordinate. Then the Greek perform some measurement at ...
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2 votes
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### Find the equation for the angle $\theta$ in which the particle leaves the semicircle. No Friction

I don't think this is wrong. $k=0$ represents the case where the large hemisphere has zero mass, so no inertia. I think you are looking for the case where the large hemisphere is "fixed", so ...
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### How does attaching a point mass to the CM of an object affect its moment of inertia about the CM?

I may be wrong, but if you're referring to these equations when you say "formulas," then your intuition is right that the moment of inertia doesn't change, despite the "total mass" ...
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### When two systems of forces acting on a rigid body are equivalent?

A theorem for a rigid body is: "Every system of forces is equivalent to a single force through an arbitrary point, plus a couple (either or both of which may be zero.)". A couple is defined ...
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