Recent content by jpo

This is a very interesting link, thanks! We need a small radial inflow turbine plus its manifold and nozzles for the purpose of building a small demonstration rig in a lab

Hello, would someone know where could one purchase a radial inflow microturbine of diameter 1 - 2 cm All I need is a contact web address or similar of the manufacturer or seller. Many thanks

An observer in a rotating frame is getting dizzy... saying this from experience But on a serious note - how does one avoid being tripped by semantics? If the 4-velocity in a rest frame is (c,0,0,0), can one express the clock rate in this frame by using the value of c? Just for the sake of...

At rest: Their spatial velocity is (0,0,0) with a norm of 0; their four-velocity is (c,0,0,0) with a norm of c

Ok, let me also ask this: If an observer is at rest, is he in any way aware of his temporal motion? Because by convention, an observer in a frame is someone, who is not aware of the motion of his own frame of reference.

An observer is at rest. A mass m is at rest too. There is no relative motion, thus the spatial velocity of m in the reference frame of the observer is (0,0,0). Now, for the time travel (or clock rate): Both the observer and m travel in the time direction with velocity c. This statement is...

Hello All, in 4-space, the position is x=(x0,x1,x2,x3), where x0=ct The question is - Can one define the clock rate in the frame of the object at rest as local clock rate = \frac{x_{0}}{t} = c Then all objects, moving with respect to this frame will have clock rates less than c. E.g., a...

elfmotat, This sounds interesting... but HOW does it follow from E=mc^{2}? As for looking at moving frames - the question again is - since E is a result of converting REST MASS, what would prompt us to consider motion, let alone moving frames? If we started looking at moving frames, we...

Nugatory, No motion is implied by E= mc^{2}, am I wrong? E appears as a result of converting REST MASS m to E. How knowing E= mc^{2} would prompt us to look at moving mass m?

I guess I am trying to reason it backwards - commonly, assuming a cosmic speed limit leads to special relativity relationships (length, time interval etc); conservation of the 4-dimensional momentum leads to E=mc^{2} Can the relativity construct be built if we start at E=mc^{2} and follow...

Hello All, Let m be a mass, equivalent to energy E such, that E=mc^{2}. Does it follow that c is the cosmic speed limit? ====================================== To say the above with more words: 1) m is a mass 2) in some process, it is established that through...

Many thanks to all and to PeterDonis for the kind reply and the detailed analysis of the box problem. PAllen, I highly appreciate your comments. This is one amazing forum.

Here is a quote from a Wikipedia article http://en.wikipedia.org/wiki/Center_of_momentum "In relativity, COM frame exists for a massive system. In the COM frame the total energy of the system is the "rest energy", and this quantity (when divided by the factor c^{2}, where c is the speed of...

This might need clarification... "If the disk were supported at its centre on set of scales" This means its weight is measured in the COM frame - thus, its mass should be M, right?

Say a disk with mass M rotates so that its periphery has velocity close to c. A stationary observer is in the COM frame. The peripheral sections of the disk will look more massive, but what about its total mass - it should still be M, right?