http://physicsworld.com/cws/article/news/2014/may/26/quantum-accelerometer-is-being-built-for-navy-submarines
"...
The device will allow submarines to pinpoint their position underwater to within 1 m after travelling one day, without having to surface to use GPS. This is much better than is possible with current accelerometers, which are accurate to within 1 km after a day's travel.
..."
I am surprised that an accelerometer can be made to be THAT accurate!
Perhaps one day, in the far future, all humans would have extremely accurate tiny accelerometers and rotation detectors implanted into our heads to artificially give us massively accurate sense of balance and incredible navigation skills?
it also says:
"..
...
The team is now working on shrinking the optical and electronic components of the accelerometer so that it can fit into about 1 m3. While this would make it suitable for naval use, the device would have to be further miniaturized – to the size of a beer can, for instance – before it could be sent down an exploratory bore hole to search for oil or other mineral deposits. Other possible applications that could emerge in a 5–10-year timeframe include "gravity scanners" that can peer into sealed containers and create density maps of their contents.
..."
-that could also be useful.
the link also mentions some research into the more theoretical physics:
"...
in another recent development in the field, physicists in Germany and the US have used atomic interferometry to measure the effects of gravity on two different atoms: rubidium and potassium. The experiment found that the acceleration due to gravity experienced by both types of atoms is the same to one part in 10 million. This is the latest verification of the universality of free fall, which is a cornerstone of Einstein's general theory of relativity. The rubidium atoms are more than twice as massive as their potassium counterparts. If they were seen to respond differently to gravity, it could point physicists towards a quantum-mechanical theory of gravity.
...."
Originally posted by humyIt's nice to see a precision test of the principle that a body falling in a vacuum accelerates independently of its mass.
http://physicsworld.com/cws/article/news/2014/may/26/quantum-accelerometer-is-being-built-for-navy-submarines
"...
The device will allow submarines to pinpoint their position underwater to within 1 m after travelling one day, without having to surface to use GPS. This is much better than is possible with current accelerometers, which are accurate to within 1 ...[text shortened]... ly to gravity, it could point physicists towards a quantum-mechanical theory of gravity.
...."
Originally posted by humyDoesn't that universal thing fail when two bodies the same mass come together?
http://physicsworld.com/cws/article/news/2014/may/26/quantum-accelerometer-is-being-built-for-navy-submarines
"...
The device will allow submarines to pinpoint their position underwater to within 1 m after travelling one day, without having to surface to use GPS. This is much better than is possible with current accelerometers, which are accurate to within 1 ...[text shortened]... ly to gravity, it could point physicists towards a quantum-mechanical theory of gravity.
...."
Like Earth has G = 9.8 M/S^2 and if another Earth mass planet was to fly down here, wouldn't the closing distance be 19.6 M/S^2?
Originally posted by sonhouseEach would be free falling in a gravity well that gives all objects (even atoms) an acceleration of 19.6 M/S^2.
Doesn't that universal thing fail when two bodies the same mass come together?
Like Earth has G = 9.8 M/S^2 and if another Earth mass planet was to fly down here, wouldn't the closing distance be 19.6 M/S^2?
The acceleration is independent of the object being accelerated, but dependent on the objects creating the gravity well.
Originally posted by sonhouseThe figure of 9.8 N/Kg only applies at the earth's surface, in your example the planets would be torn apart by tidal forces long before then. The force from earth 1 exerted on earth 2 is -GM^2/r^2 (and vice versa) so the acceleration of earth 2 is -GM/r^2. But this is relative to the centre of mass of the two earth system, so the rate at which their relative velocity changes is -2GM/r^2.
Doesn't that universal thing fail when two bodies the same mass come together?
Like Earth has G = 9.8 M/S^2 and if another Earth mass planet was to fly down here, wouldn't the closing distance be 19.6 M/S^2?
In the case of an atom falling towards the earth, the centre of mass of the earth atom system is experimentally indistinguishable from the centre of mass of the earth, so the Earth's acceleration is virtually zero and the atom's acceleration is 9.8m/s^2.
- Joined
- 31 May 06
- Moves
- 1795
Originally posted by DeepThoughtAn incoming planet would only be torn apart by tidal forces if it's orbiting the earth.
The figure of 9.8 N/Kg only applies at the earth's surface, in your example the planets would be torn apart by tidal forces long before then. The force from earth 1 exerted on earth 2 is -GM^2/r^2 (and vice versa) so the acceleration of earth 2 is -GM/r^2. But this is [b]relative to the centre of mass of the two earth system, so the rate at which t ...[text shortened]... he earth, so the Earth's acceleration is virtually zero and the atom's acceleration is 9.8m/s^2.[/b]
If, it's coming [effectively] strait in it just piles into us.
Originally posted by googlefudgeHardly, the atmosphere persists out to about 10,000 km, the orbit there is still some atmosphere. There is also the solar wind and there are gravitational perturbations from the moon and the sun. There is just too much going on for a precision test of the principle, which the article said was to one part in 10 million.
Yes... We do that all the time... We call them satellites.
They are all constantly falling in a vacuum.
Originally posted by DeepThoughtSurely the orbits of the planets are known to that accuracy?
Hardly, the atmosphere persists out to about 10,000 km, the orbit there is still some atmosphere. There is also the solar wind and there are gravitational perturbations from the moon and the sun. There is just too much going on for a [b]precision test of the principle, which the article said was to one part in 10 million.[/b]
Originally posted by googlefudgeSurely the near edge would be accelerated so much faster than the outer edge that it would get torn apart? It would only start piling into us once contact is made, but prior to that it should experience very significant tidal forces.
An incoming planet would only be torn apart by tidal forces if it's orbiting the earth.
If, it's coming [effectively] strait in it just piles into us.
Originally posted by twhiteheadBut with 12,000 km diameter planets coming straight at each other, the final approach would be coming so fast I doubt there would be much TIME for such things as tidal stretching. It would be an awesome site though🙂
Surely the near edge would be accelerated so much faster than the outer edge that it would get torn apart? It would only start piling into us once contact is made, but prior to that it should experience very significant tidal forces.
They say that is how we got our moon, a Mars sized body whacking into Earth and leftover debris forming the moon. And I understand it was less than 25,000 km from Earth ATT and receding at about 2 cm per year.
Originally posted by twhiteheadThe positions of the planets probably are known to that precision - since that is measured from the solar system's centre of mass. Mars' orbital speed is 24km/s, one part in 10 million of that is 2.4mm/s I doubt it's velocity is known to that precision. Getting to actual accelerations, the acceleration due to the Sun's gravity for Mars' at Aphelion is 21 mm/s^2. Which means that they'd have to be able to measure a difference in acceleration of the order of nanometres per second per second to test to the same precision.
Surely the orbits of the planets are known to that accuracy?
The caveat to what I'm saying is that the group who did the gravity test gave their result in terms of the Eötvös ratio and I have no idea what that is. I looked up the abstract, by following the above link you can get to it at http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.203002
We simultaneously measure the gravitationally induced phase shift in two Raman-type matter-wave interferometers operated with laser-cooled ensembles of Rb87 and K39 atoms. Our measurement yields an Eötvös ratio of eta_{Rb,K} =(0.3±5.4)×10^-7. We briefly estimate possible bias effects and present strategies for future improvements.
Does anyone know what an Eötvös ratio is?
Originally posted by DeepThoughtNo, but I'm going to remember that for Scrabble!
The caveat to what I'm saying is that the group who did the gravity test gave their result in terms of the Eötvös ratio and I have no idea what that is. I looked up the abstract, by following the above link you can get to it at http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.203002We simultaneously measure the gravitationally induc ...[text shortened]... d present strategies for future improvements.
Does anyone know what an Eötvös ratio is?
Originally posted by sonhouseRelative velocity is not important - unless we take relativity into account, but assume that we are not dealing with relativistic speeds. Just before impact, the near sides of the planets would be experiencing significantly more acceleration than the far sides. Both the planets would disintegrate.
But with 12,000 km diameter planets coming straight at each other, the final approach would be coming so fast I doubt there would be much TIME for such things as tidal stretching. It would be an awesome site though🙂