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.
4,511 questions
1
vote
1
answer
126
views
Definition of reference system in the context of General Relativity [closed]
I'm in trouble with the definition of reference system in the context of General Relativity intended as coordinate chart (i.e. no frame field).
Various sources define it as a one-to-one smooth mapping ...
- 207
2
votes
2
answers
123
views
Why do we conclude that gravity is fictitious force from equivalence principle?
I read about equivalence principle. I tried to understand Einstein's thought experiment with elevator and I can't understand why we compare elevator in the space and elevator on the surface of the ...
- 653
-3
votes
0
answers
38
views
Relative motion interesting question [closed]
A rabbit begins at the origin, and the fox begins at the point (0,-a). The rabbit begins running east, with a constant speed v(x) along positive x axis. At the same time, the fox begins chasing the ...
0
votes
3
answers
54
views
Energy required for round trip when rowing a boat with and without current
Suppose a person can row a boat at a certain constant speed in still water. Suppose that they make a certain round trip in still water. The same round trip would take a longer time if there's a ...
- 259
-4
votes
1
answer
116
views
Physical significance of $(m_x,m_y)=(\frac{\sum m_i x_i}{\sum x_i}, \frac{\sum m_i y_i}{\sum y_i})$ [closed]
What is the physical significance of $$(m_x,m_y)=(\frac{\sum m_i x_i}{\sum x_i}, \frac{\sum m_i y_i}{\sum y_i})~?$$
The equation looks like the one of center of mass. There we calculate, the point ...
1
vote
1
answer
41
views
Clarification on angular velocity of rolling body
In writing kinetic energy of a rolling with respect of COM and with respect to Instantaneous axis of rotation, I have seen books using same angular velocity in both cases, but why? Since we are ...
- 11
-1
votes
3
answers
149
views
Can someone explain it to me? Why a rotating system is not an inertial system? [closed]
Can someone explain it to me? Why a rotating system is not an inertial system?
I mean a point observer on the axis of rotation with a local frame of reference.
Constant angular momentum
And
...
- 7
8
votes
4
answers
576
views
On the definition of rest frame in special & general relativity
In the context of special & general relativity there exists the notion of "rest frame" w.r.t. an object or an observer.
The latter are represented in spacetime by a timelike worldline (...
- 207
0
votes
1
answer
104
views
Relation between momentum density and energy flux for a non-inertial observer
I am trying to reconstruct the observer–dependent interpretation of the stress–energy tensor starting only from its definition as a flux of four-momentum.
I only want to talk about special relativity (...
- 91
8
votes
2
answers
324
views
Is the tetrad formalism of general relativity related to the equivalence principle?
I've been recently studiying Wald's General Relativity, and stumbled upon the tetrads method for working on General Relativity. The author states that this method is just "a mathematical trick&...
- 2,175
1
vote
1
answer
132
views
What is an inertial coordinate system? [duplicate]
A lot of posts have been made about the nature of inertial coordinate systems, but I did not find one that answered my doubts. I have a masters in math and am starting my PhD in mathematical physics ...
- 111
4
votes
5
answers
615
views
A configuration acts through its centre of mass -- elementary school version
I am trying to explain some lever physics at elementary school level. In particular I want a good visualisation of why a compound object behaves like a point particle at its centre of gravity.
Assume ...
- 399
13
votes
9
answers
3k
views
Where is the center of mass of a donut-shaped object?
I understand that the center of mass of an object is the average position of its mass distribution and for symmetrical objects like cube or sphere I get it
But when I consider a torus the center of ...
- 304
-5
votes
1
answer
86
views
How can proper time differ for particles traversing the same spatial path if local processes occur at the same rate? [closed]
As an amature and not a math wiz, I often find the ontology of physics more interesting than the formalism. Lately, I have been trying to understand how relativity causes different proper times when ...
1
vote
3
answers
172
views
Can a Distance Derived from Redshift be Seen as a “True” Distance if we Consider a Distant Galaxy to be Stationary Relative to the Milky Way galaxy? [closed]
A distant galaxy is observed by an Earth observer. The observer considers themself to be stationary and the galaxy to be moving away relative to the observer.
The value of the redshift of the galaxy ...
- 59