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thequantumcat
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I can't seem to wrap my head around it: if an object is moving at speed v in frame S, and its observed to move at speed v' in S', what is the relationship?
PeroK said:This is homework, so you need to give it your best shot. Are you stuck on all of these questions?
PAllen said:There appears to be some missing explanation of the problem context (that you didn’t quote?). Specifically, it appears you are to assume S‘ is moving at v in the x direction per S.
In the non-relativistic limit we have ##u = u' + v##. Note that these are all velocities, not speeds.thequantumcat said:So then is this correct:
S is at rest--inertial frame.
u is speed of object in that frame
S' is "moving observer" and its speed is v
u' is the speed of object in S' (i.e speed as seen by this frame)
In that case, the velocity formula would be:
u = (u' - v)/(1-(u'v/c^2)) ??
I am confused by this part really. Which quantity goes where?
I always get confused...
What is the difference between "speed" and "velocity"? I ask, because I am a non-native English speaker, and dictionaries translate both to the same set of words:PeroK said:Note that these are all velocities, not speeds.
Velocity means the vector. Speed is its magnitude. I seem to recall reading on here that this convention was established by one textbook in the 1920s (or something like that), so this may not apply to older texts.Sagittarius A-Star said:What is the difference between "speed" and "velocity"?
What does who mean by that?etotheipi said:Also, what do they mean by 'massless energy' and 'massless momentum'?
Ibix said:What does who mean by that?
I've never heard the term before, but I assume they mean energy/momentum taken away by massless particles.etotheipi said:Also, what do they mean by 'massless energy' and 'massless momentum'?
...which is an image, which is why "find in page" only found your post. Sorry.etotheipi said:In the problem in post #3
Me neither. Energy or momentum per unit mass, perhaps? Or kinetic energy ##(\gamma-1)mc^2##, although what massless momentum would be in that case I don't know.etotheipi said:I don't quite know what that means...
That makes more sense. Something like a nuclear fission process where you get energy carried away as radiation.PeroK said:I've never heard the term before, but I assume they mean energy/momentum taken away by massless particles.
vanhees71 said:Once more, the confusion seems to be due to the use of old-fashioned ideas which were long abandoned in the physics community but still being used in popular-science writings and (which is a crime) even in some textbooks. One such things are the various relativistic masses.
DrStupid said:Where do you see relativistic masses?
vanhees71 said:In #1, or how do you interpret "massless energy".
Vanadium 50 said:A useful tool for derailing threads.
vanhees71 said:If you agree with all this confusion, could you then explain to me, what "massless energy" and "massless momentum" is? I interpreted this as if this might be a language stemming from usual wrong concepts related to mass.
vanhees71 said:Sigh! I knew that it is about the oldfashioned concept of mass :-((. Mass is invariant mass (a scalar) and nothing else, and energy is energy (the temporal component of the energy-momentum four-vector).
Special relativity is a theory developed by Albert Einstein that describes the relationship between space and time in the absence of gravity. It states that the laws of physics are the same for all observers in uniform motion and that the speed of light is constant for all observers.
Special relativity explains velocity by stating that the speed of light is the maximum speed at which all objects can move. As an object approaches the speed of light, its mass increases and time slows down, making it impossible to reach the speed of light.
Special relativity only applies to objects in uniform motion in the absence of gravity, while general relativity applies to all objects in any type of motion, including those under the influence of gravity. General relativity also takes into account the curvature of space and time.
Special relativity has had a significant impact on our understanding of the universe by providing a new framework for understanding the laws of physics and how they apply to objects in motion. It has also led to the development of technologies such as GPS, which rely on precise measurements of time and space.
Special relativity has been extensively tested and has consistently been shown to accurately describe the behavior of objects in motion. However, it is a scientific theory and therefore can never be definitively proven. It is constantly being refined and tested through experiments and observations.