If I can just stay alive for another 12 years, Steve!
Dragonfly - a multi-rotor vehicle with eight rotors that flies like a large drone. It will take advantage of Titan’s dense atmosphere – four times denser than Earth’s.
During the Battle of Britain, the average strength of fighter command was 1,326 Hurricanes compared to 957 Spitfires.
a) You obviously don't count yourself as a physicist?
b) concerning black holes it is, as you say, a hypothesis. Because 1. there is no scientific observation of black holes, because 2. these are only an imagination, a reification of the big bangings of "indifferent" only;-)
Be glad, he meets these;-)
I'm slowly rebuilding the Airfix kits I built as a boy.
I've still to get round to my Mosquito:
I reckon we are sort of on topic with aircraft as they are gravity-defying machines!
My next door neighbour, Ray, was a ground crew Mosquito engineer:
The man can fix anything greasy and mechanical! I don't know how he did it! But he did it.
These days he still rebuilds cars:
What is not to like in one of his recent engineering projects?
A superb restoration. My dear sister nearly killed me in one of these Cars. It was a close Head-on scrape! I ducked. 🙂
The man can fix anything greasy and mechanical! I don't know how he did it! But he did it.
These days he still rebuilds cars:
What is not to like in one of his recent engineering projects?
A superb restoration. My dear sister nearly killed me in one of these Cars. It was a close Head-on scrape! I ducked. 🙂
Ray and your good friend Finn, "who is expert on the nature of the Rolls-Royce Spitfire V-12 27L Merlin engine", must make great drinking partners!
I'm not quite sure they "lose" or "gain" any energy.
I believe this is the "observed" case from an observation from and independent coordinate system. But within the coordinate system where the photons are travelling there is no gain or loss.
It's all relative to the position of the observer.
I was considering photons in a gravitational field.
Certainly, a photon which is red-shifted by the expansion of space does not lose energy.
Suppose an observer travelling along with a distant galaxy sees a photon in the yellow part of the spectrum. By contrast, an observer situated at a point from which the galaxy is receding will see the same photon in the red part of the spectrum.
However, the red-shifted photon has not lost any energy. The principle of conservation of energy is not violated since the two observers are making their measurements in different reference frames.
Last edited:
First off... definition... A perpetual motion machine is a hypothetical machine that can do work infinitely without an external energy source
According to Newton, F(t)=ma(t). So long as there are no forces on the rock (m), that is, F=0, then a=0.
That means the p(t)=mv(t). Since v' = 0 ( that would be a ), then p(t) = K , a constant. Thus we see a conservation of momentum. So, the energy of the rock moving in space is constant.
Now, you could argue that the "energy" of the rock needs to be calculated in terms of its coordinate system.. (*) And measurements of that energy will vary depending on the time-spatial relationship between the rock and the observer doing the measurements. It could definitely be possible that the energy of the rock might be variable from the observer's point of view... but within the rock's environment its momentum is indeed constant.
Now with this out of the way, the answer to your question.... to do work, an object must be transferring energy... thus a lump of rock moving through space with constant momentum, and with no forces acting upon it, can not be doing work... thus it is NOT perpetual motion.
(*) The true crux of the matter.
It can be confusing to think about the conservation of energy and measurements made from different reference frames.
You make it sound as if I did not know the answer to the question I directed at vishal!
The equations for the black hole are actually obvious... you just take the value of gravity to a given limit and you get the Event Horizon.
What happens inside is open for conjecture.
Nonetheless, the existence of phenomena that are predicted by our current model of "black holes" has been measured. Stuff like rotation of X-ray jets coming out, axially, from the accretion disk, for example.
I think I need to call Scotty and get beamed up to the living room so I can warm up the stereo.
A little bit of that old push-pull atmospheric compression-rarefaction at audio frequencies is called for.
A little bit of that old push-pull atmospheric compression-rarefaction at audio frequencies is called for.
The reference frame is very useful. Many math problams become much easier to solve if one changes the reference frame (coordinate system is a subset).
dave
Consider a thought experiment involving an object being dropped from a tower.
What if the total mass of the object were converted into energy at the bottom and returned to the top of the tower as a photon?
Unless the photon loses as much energy in climbing against gravity as the mass gained in falling, energy would not be conserved.
Don't ask me about the frame of reference though! 😀
So, we had to take this class on coordinate transformations... a whole senior semester. The final was the professor drawing an object of revolution on the board and telling us to write EVERYTHING we could think about it.
It was an obloid, two hour long test.
So, I started writing..... around the 21st page of equations ( 75 minutes...) I realized that I had put a '-' instead of a '+' in the very first set of equations.... it was a hyperboloid... yikes!
So, I put an ellipsis on my equations, turned the page and wrote, BIG, VERY BIG... WHOOPS! and presented my new first set of equations with a '+' instead of a '-' and furiously continued. (*)
I got to almost 45 pages..... before time ran out.
The prof gave me an A+. He noted that he saw my error at very beginning but kept looking through the paper, when he saw that I caught it... he just glanced at the rest of the derivations and figured I knew what I was doing.
Yes, coordinate transformations are fundamental to doing Physics. What would we do without matrices?
(*) It helped that we put numbers on each important equation within and at the end of each derivation/solution.... so it was a matter of writing stuff like: equation (3) was wrong... it should have been as in equation (54) below...