Orbits: What is Correct?

January 17th, 2018 at 3:37:56 AM permalink
odiousgambit
Member since: Oct 28, 2012
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Does anyone know for sure the answer to this:

Take the well known thought experiment of the shot out of the cannon; if the velocity is unlimited, low velocity will have the object return to Earth, but if the object is at higher and higher speed, eventually it keeps "falling" indefinitely, or goes into orbit.

Imagine it has a conical shape and does go into orbit, making a perfect circle. What would normally be maintained as its aspect in that orbit? Would it start [A ]with its base perpendicular to the Earth, base back towards the cannon ... then quarter way around the Earth, have the base point towards the Earth ... halfway around perpendicular to Earth ... three quarters around have the conical tip pointed to the Earth ... then go back to original aspect?

Or , would the projectile maintain throughout an unchanging aspect, with the base perpendicular to Earth and the conical tip always pointed along the line that defines the circular orbit?

I say B, and furthermore if there were astronauts in the projectile [it's big!] I think even though an observer above the Earth looking down on with full view of the circle would see the aspect change constantly from THAT perspective. The astronauts without a window would be unable to do any experiment that would prove that their aspect was changing in any way even though from the perspective of the observer above the circle it is changing. That would include experiments using a gyroscope.

*yes you may need to call the guys with the straight jackets and have me sent to the funny farm
Mustard:You like Kipling, Miss Scarlet? Sure, I'll eat anything [from movie]
January 17th, 2018 at 4:48:54 AM permalink
OnceDear
Member since: Nov 21, 2017
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Quote: odiousgambit
Does anyone know for sure the answer to this:
It all depends on the rotational momentum that the vehicle has. So it maybe that its is constantly pointing towards earth like the moon's 'face' or it might be that it seems to be spinning quickly or slowly
January 17th, 2018 at 5:07:36 AM permalink
odiousgambit
Member since: Oct 28, 2012
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They call the moon's constant face "tidal locking" which a smaller object tends to go to orbiting a larger one. In that case the moon could have been initially rotating like the earth does around the sun and it is believed it still would have eventually been locked into what it is.

Unfortunately I think that confuses the matter. In case you haven't guessed, this has come up with me pondering the analemma thing.

shoot me
Mustard:You like Kipling, Miss Scarlet? Sure, I'll eat anything [from movie]
January 17th, 2018 at 10:55:06 AM permalink
boymimbo
Member since: Mar 25, 2013
Threads: 5
Posts: 732
Quote: odiousgambit
Does anyone know for sure the answer to this:

Take the well known thought experiment of the shot out of the cannon; if the velocity is unlimited, low velocity will have the object return to Earth, but if the object is at higher and higher speed, eventually it keeps "falling" indefinitely, or goes into orbit.

Imagine it has a conical shape and does go into orbit, making a perfect circle. What would normally be maintained as its aspect in that orbit? Would it start [A ]with its base perpendicular to the Earth, base back towards the cannon ... then quarter way around the Earth, have the base point towards the Earth ... halfway around perpendicular to Earth ... three quarters around have the conical tip pointed to the Earth ... then go back to original aspect?

Or , would the projectile maintain throughout an unchanging aspect, with the base perpendicular to Earth and the conical tip always pointed along the line that defines the circular orbit?

I say B, and furthermore if there were astronauts in the projectile [it's big!] I think even though an observer above the Earth looking down on with full view of the circle would see the aspect change constantly from THAT perspective. The astronauts without a window would be unable to do any experiment that would prove that their aspect was changing in any way even though from the perspective of the observer above the circle it is changing. That would include experiments using a gyroscope.

*yes you may need to call the guys with the straight jackets and have me sent to the funny farm


Assuming it is completely above the atmosphere, The orbit is governed by Fg = G m1 m2 / r^2. For it to be a "perfect circlle", the perpendicular velocity would have to completely offset this force.

As for the aspect of the object, there is no reason that in the short term it would change meaning that it would maintain its absolute aspect in space and that an observer in various parts of the earth would see the object in different aspects.
January 17th, 2018 at 11:23:48 AM permalink
Dalex64
Member since: Mar 8, 2014
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I think the base-end would end up "down" towards the earth, eventually.

initially there would be no aspect change, so the pointy end would always point in the same direction, but the larger-end would have more mutual attraction so, the cone would start to rotate. as that rotation imparts some rotational inertia, the base would actually rotate past straight towards the earth, slow down, and be drawn back again, slowly oscillating with smaller and smaller swings, until the object was finally heavy-end down towards the earth.
"Everyone is entitled to his own opinion, but not to his own facts." Daniel Patrick Moynihan
January 17th, 2018 at 12:35:41 PM permalink
odiousgambit
Member since: Oct 28, 2012
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now, if I have you two correctly, you are going with "A" or something similar and certainly not "B".

I asked a question and didn't just assert that "B" is correct, because I am not sure. However, remember how easy it is for intuition to get it all wrong when it comes to gravity. Intuition would say Galileo was all wrong to say a heavy object falls at the same rate as a light object, but he proved he was right. And objects in orbit are essentially falling; they are weightless, and the astronauts float.

PS: I did not mean to suggest a circular orbit was to be expected, but just wanted to pose a circular orbit to avoid the complications of an elliptical one.
Mustard:You like Kipling, Miss Scarlet? Sure, I'll eat anything [from movie]
January 17th, 2018 at 12:40:41 PM permalink
boymimbo
Member since: Mar 25, 2013
Threads: 5
Posts: 732
Quote: Dalex64
I think the base-end would end up "down" towards the earth, eventually.

initially there would be no aspect change, so the pointy end would always point in the same direction, but the larger-end would have more mutual attraction so, the cone would start to rotate. as that rotation imparts some rotational inertia, the base would actually rotate past straight towards the earth, slow down, and be drawn back again, slowly oscillating with smaller and smaller swings, until the object was finally heavy-end down towards the earth.


Eventually correct.
January 17th, 2018 at 12:45:27 PM permalink
odiousgambit
Member since: Oct 28, 2012
Threads: 89
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Quote: boymimbo
Eventually correct.


definitely do not think it would wind up heavy end down unless it started that way, due to being weightless
Mustard:You like Kipling, Miss Scarlet? Sure, I'll eat anything [from movie]
January 17th, 2018 at 1:31:07 PM permalink
Dalex64
Member since: Mar 8, 2014
Threads: 2
Posts: 2356
Weebles wouldn't wobble if the heavy side didn't end up down.

One side of the moon faces the earth because of tidal locking. WHICH side is because of the uneven mass distribution of the moon. The heavier side faces us.

https://en.wikipedia.org/wiki/Tidal_locking

https://spaceflightsystems.grc.nasa.gov/education/rocket/moon.html

https://space.stackexchange.com/questions/22520/which-side-of-the-moon-faces-earth-the-heavy-side-or-the-lighter-side

https://www.quora.com/Why-do-we-always-see-the-same-side-of-the-moon-from-Earth
"Everyone is entitled to his own opinion, but not to his own facts." Daniel Patrick Moynihan
January 17th, 2018 at 2:12:01 PM permalink
odiousgambit
Member since: Oct 28, 2012
Threads: 89
Posts: 2205
Quote: Dalex64
One side of the moon faces the earth because of tidal locking.


as mentioned upthread, I think the phenomenon of tidal locking unfortunately confuses this issue rather than enlightens it. In other words, doesn't pick B over A or vice versa in the original question. However, you may be right that eventually the heaviest portion faces down on all satellites ... that could really be a matter of centuries or something though is my thinking.

In a tidal lock, it seems the orbiting object originally could be expected to have rotation on an axis that eventually was made to synchronize [edit].

I sometimes feel the internet now has the answers to everything, and maybe it does on this, but it was not easily found so far. I am hoping someone knows here and can really convince.
Mustard:You like Kipling, Miss Scarlet? Sure, I'll eat anything [from movie]