Orbit
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Speed? We are talking physics here. Leave speed to the Engineers. Velocity, please! Speed is scaler quantity, velocity is a vector quantity. Example... The electron travelling from the light switch to the bulb has a very low velocity, yet it's speed is close to c.
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]
Dalek Dave wrote:
Speed is scaler quantity
Is it only scalar when it's not climbing a mountain?
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Dalek Dave wrote:
terminal gravitational velocity
You really should choose better pages from the Google result.
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Mark_Wallace wrote:
A stable orbit is one where enough (constant) lateral force is provided for the falling object for it to never hit the floor.
Firstly it is called tangential velocity. Second...CONSTANT force would be an acceleration. Remember Newton's Laws? All it needs is a single force applied once to give the required velocity, conservation of angular momentum and basic physics mean that once orbit is achieved, no further force is necessary.
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]
Dalek Dave wrote:
Firstly it is called tangential velocity.
It's called whatever I bloody well decide to call it, especially in the context of a discussion board, where such frippery is not relevant. Google again, you'll find that there are several ways of describing/naming it.
Dalek Dave wrote:
Second...CONSTANT force would be an acceleration.
I don't see what point you're trying to make, here, but it's wrong, nonetheless. If a constant force is used to overcome friction, there's no acceleration.
Dalek Dave wrote:
All it needs is a single force applied once to give the required velocity, conservation of angular momentum and basic physics mean that once orbit is achieved, no further force is necessary.
Bollocks. If there's any friction at all, the angular momentum is affected, and not even the remotest parts of space contain an absolute vacuum.
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Aha! That was going to be my next question. You seem to know more about these sorts of things than one should so I thought there might be some sort of formal qualification in there.
Regards, Rob Philpott.
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If you have an Android device there is a game called Orbit that you should be able to get from the google play store for free. It's a simple game and all you need to do is get satellites into orbit around a planet - it's not easy and quite addictive(so beware...).
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
That sounds cool. Perhaps a better use of my time.
Regards, Rob Philpott.
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No. (Get some brain plasters ready). The Moon orbits the earth. It does so because the Earth is pulling it gravitationally. The Moon would carry on in a straight line if it were not for this pull so it is therefore ACCELERATING toward the Earth. However, because it is now travelling slightly faster, the orbit diameter increases. Therefore, and this is where non-physicists have a conniption fit, it is constantly moving away from the Earth as it constantly accelerates toward it. The reason it does not crash into the Earth is because the tangential velocity is greater than the terminal gravitational velocity. Remember that virtually no orbits are circular, so be mindful of Kepler's Laws of Motion. The nearer something is, the fast it has to orbit to avoid collision, which is why the inner planets orbit much quicker than the outer ones. And in an elliptical orbit, the orbiting body moves much more quickly as it passes the major loci than at other times.
Rob Philpott wrote:
So, there must be an exact distance where these two opposing concepts balance themselves out and things orbit happily.
No, all things in the universe are gravitationally attracted to all other things, and the laws of orbital mechanics show there are a vast array of areas of orbital possibility. Think about how relatively small our galaxy is, and how far away it is from all the other galaxies. They are all (with the exception of Andromeda) flying away from us at great speed. And yet, our 'Local Group' is orbiting a centre of gravity that is itself being pulled, along with the rest of our cluster, toward The Great Attractor.
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]
Dalek Dave wrote:
The Moon orbits the earth.
<<MaximumPedantryInPedanticPedantMode>>
Actually, no. The Earth and Moon both orbit the Earth/Moon barycentre, approximately 2,600 miles from the centre of the Earth. ;P
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No. (Get some brain plasters ready). The Moon orbits the earth. It does so because the Earth is pulling it gravitationally. The Moon would carry on in a straight line if it were not for this pull so it is therefore ACCELERATING toward the Earth. However, because it is now travelling slightly faster, the orbit diameter increases. Therefore, and this is where non-physicists have a conniption fit, it is constantly moving away from the Earth as it constantly accelerates toward it. The reason it does not crash into the Earth is because the tangential velocity is greater than the terminal gravitational velocity. Remember that virtually no orbits are circular, so be mindful of Kepler's Laws of Motion. The nearer something is, the fast it has to orbit to avoid collision, which is why the inner planets orbit much quicker than the outer ones. And in an elliptical orbit, the orbiting body moves much more quickly as it passes the major loci than at other times.
Rob Philpott wrote:
So, there must be an exact distance where these two opposing concepts balance themselves out and things orbit happily.
No, all things in the universe are gravitationally attracted to all other things, and the laws of orbital mechanics show there are a vast array of areas of orbital possibility. Think about how relatively small our galaxy is, and how far away it is from all the other galaxies. They are all (with the exception of Andromeda) flying away from us at great speed. And yet, our 'Local Group' is orbiting a centre of gravity that is itself being pulled, along with the rest of our cluster, toward The Great Attractor.
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]
Dalek Dave wrote:
The Moon orbits the earth.
<<MaximumPedantryInPedanticPedantMode>> Actually, no. The Earth and Moon both orbit the Earth/Moon barycentre, approximately 2,600 miles from the centre of the Earth. ;P <</MaximumPedantryInPedanticPedantMode>>
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Dalek Dave wrote:
The Moon orbits the earth.
<<MaximumPedantryInPedanticPedantMode>> Actually, no. The Earth and Moon both orbit the Earth/Moon barycentre, approximately 2,600 miles from the centre of the Earth. ;P <</MaximumPedantryInPedanticPedantMode>>
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"Terminal velocity" has nothing to do with orbits; it's about the effect of atmospheric friction on falling bodies, so the silly term is inherently confusing.
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Pete O'Hanlon wrote:
You're correct in thinking that there's a sweet spot, and also that orbits are transitory
Er...I think not. There are millions of possible orbits, billions, trillions... There is no 'Sweet spot', so long as the orbiting body has a tangential velocity between the upper and lower ranges then it will orbit. If the 'sweet spot' existed then orbits would be rare rather than exceedingly commonplace. As for the transitory nature, well, yes, I suppose the Universe will end one day. In a two satellite system the harmonics are such that eventually one of the orbiting bodies will crash into the planet (this is inevitable owing to gravitational harmonics), one of the bodies slows the other, causing it to fall in, and 'steals' that angular momentum for itself, thus speeding up and moving outward. Once the collision takes place the system reverts to a stable single orbit system. In the Earth Moon system for example, the moon is racing away at the rate of several centimetres a year, but it will be BILLIONS of years before this becomes a problem. In fact the sun will have shrunk to a brown dwarf which will be rather more problematic than the prospect of losing a moon.
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]
Dalek Dave wrote:
Er...I think not.
There are millions of possible orbits, billions, trillions...
There is no 'Sweet spot', so long as the orbiting body has a tangential velocity between the upper and lower ranges then it will orbit.
If the 'sweet spot' existed then orbits would be rare rather than exceedingly commonplace.Err, I think so. The sweet spot is a huge area, I didn't claim it wasn't. It's that point where gravity is strong enough to exert an influence on the other body that causes it to move into orbit rather than continuing in a straight line past the exerting body.
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Mark_Wallace wrote:
A stable orbit is one where enough (constant) lateral force is provided for the falling object for it to never hit the floor.
Firstly it is called tangential velocity. Second...CONSTANT force would be an acceleration. Remember Newton's Laws? All it needs is a single force applied once to give the required velocity, conservation of angular momentum and basic physics mean that once orbit is achieved, no further force is necessary.
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]
Dalek Dave wrote:
All it needs is a single force applied once to give the required velocity, conservation of angular momentum and basic physics mean that once orbit is achieved, no further force is necessary.
While I see what you are trying to say, a constant force (the gravitational attraction of the two bodies) is required for an orbit. The mass of moon and earth are (essentially) both constant. So we have a value of m to play with. The velocity of the moon is constantly changing, so it is accelerating. So we have a value of a F = ma if m and a have values other than zero, then F must have a value. So there is a force. Not just 'a single force applied once' Once cold postulate that there must be an initial force beyond the gravitational attraction between the two bodies, in order to give them some relative motion other than directly toward one another, but with the majority of natural satellites, this initial velocity would have been imparted and ganged over millennia by the gravitation attraction of all the other bodies around. Assuming any two bodies with mass, close enough for gravity to have an effect, that are not stationary relative to one another, they must end up in one of three states (short term) 1. They collide 2. They fly apart never to meet again 3. They orbit one another Case 1 is obvious (although it may follow case 2) Case 2 happens if their relative velocity is greater than the escape velocity Case 3 happens for all other cases.
MVVM# - See how I did MVVM my way ___________________________________________ Man, you're a god. - walterhevedeich 26/05/2011 .\\axxx (That's an 'M')
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Dalek Dave wrote:
Firstly it is called tangential velocity.
It's called whatever I bloody well decide to call it, especially in the context of a discussion board, where such frippery is not relevant. Google again, you'll find that there are several ways of describing/naming it.
Dalek Dave wrote:
Second...CONSTANT force would be an acceleration.
I don't see what point you're trying to make, here, but it's wrong, nonetheless. If a constant force is used to overcome friction, there's no acceleration.
Dalek Dave wrote:
All it needs is a single force applied once to give the required velocity, conservation of angular momentum and basic physics mean that once orbit is achieved, no further force is necessary.
Bollocks. If there's any friction at all, the angular momentum is affected, and not even the remotest parts of space contain an absolute vacuum.
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Mark_Wallace wrote:
not even the remotest parts of space contain an absolute vacuum
I have a Dyson in the Utility. That's supposed to be the absolute best.
I was brought up to respect my elders. I don't respect many people nowadays.
CodeStash - Online Snippet Management | My blog | MoXAML PowerToys | Mole 2010 - debugging made easier -
Mark_Wallace wrote:
not even the remotest parts of space contain an absolute vacuum
I have a Dyson in the Utility. That's supposed to be the absolute best.
I was brought up to respect my elders. I don't respect many people nowadays.
CodeStash - Online Snippet Management | My blog | MoXAML PowerToys | Mole 2010 - debugging made easierHe should make a spherical model.
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Dalek Dave wrote:
All it needs is a single force applied once to give the required velocity, conservation of angular momentum and basic physics mean that once orbit is achieved, no further force is necessary.
While I see what you are trying to say, a constant force (the gravitational attraction of the two bodies) is required for an orbit. The mass of moon and earth are (essentially) both constant. So we have a value of m to play with. The velocity of the moon is constantly changing, so it is accelerating. So we have a value of a F = ma if m and a have values other than zero, then F must have a value. So there is a force. Not just 'a single force applied once' Once cold postulate that there must be an initial force beyond the gravitational attraction between the two bodies, in order to give them some relative motion other than directly toward one another, but with the majority of natural satellites, this initial velocity would have been imparted and ganged over millennia by the gravitation attraction of all the other bodies around. Assuming any two bodies with mass, close enough for gravity to have an effect, that are not stationary relative to one another, they must end up in one of three states (short term) 1. They collide 2. They fly apart never to meet again 3. They orbit one another Case 1 is obvious (although it may follow case 2) Case 2 happens if their relative velocity is greater than the escape velocity Case 3 happens for all other cases.
MVVM# - See how I did MVVM my way ___________________________________________ Man, you're a god. - walterhevedeich 26/05/2011 .\\axxx (That's an 'M')
I see what you say. Obviously the Gravity would be a constant force, I was referring to the force applied to impart a vector other than toward the other body. Try working out the orbits of a three body system. Seriously difficult (and chaotic) and, sadly well beyond my limited ability.
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]
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Dalek Dave wrote:
Firstly it is called tangential velocity.
It's called whatever I bloody well decide to call it, especially in the context of a discussion board, where such frippery is not relevant. Google again, you'll find that there are several ways of describing/naming it.
Dalek Dave wrote:
Second...CONSTANT force would be an acceleration.
I don't see what point you're trying to make, here, but it's wrong, nonetheless. If a constant force is used to overcome friction, there's no acceleration.
Dalek Dave wrote:
All it needs is a single force applied once to give the required velocity, conservation of angular momentum and basic physics mean that once orbit is achieved, no further force is necessary.
Bollocks. If there's any friction at all, the angular momentum is affected, and not even the remotest parts of space contain an absolute vacuum.
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Mark_Wallace wrote:
It's called whatever I bloody well decide to call it, especially in the context of a discussion board, where such frippery is not relevant.
Google again, you'll find that there are several ways of describing/naming it.+5 purely on that! I raise a :java: in your direction
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My dilemma today is why do things orbit other things - moons, planets, satellites, that sort of thing. If something in orbit around the earth gets too close it falls to the ground/burns up etc. Too far away and the thing will just keep going under its own momentum and disappear into space. So, there must be an exact distance where these two opposing concepts balance themselves out and things orbit happily. But for that to work, everything would have to be exact, which it isn't. Maybe orbits are just transitory things which happen for a bit but they're the only things we can see. If everything just drifted all over the place in space there wouldn't really be any structure. What's going on?
Regards, Rob Philpott.
Rob Philpott wrote:
But for that to work, everything would have to be exact, which it isn't.
It is [almost] the moon is actually spiralling out (about 1cm a year IIRC, a fact on discovered when NASA put mirrors on the moon so we could more accurately measure distance using LASERs. Which is beyond freakin' cool). The basic principle fo a circular orbit is as DD describes: The moon is being pulled (accelerated) towards the Earth, but it's momentum is at 90°, the accelration changes the velocity (the direction component, not the speed) continually in this way so the moon follows a circular path. The situation is slightly more complicated inm reality: the orbit is an elipse (so the momentum isn't always 90° and the speed of the moon slows down and speeds up depending where in the orbit it is. For a real mind-bendy situation, the moon and the Earth both orbit their combined centre of gravity[^], so the earth will appear to wobble when viewed from a distance: the same thing happens when a planet orbits it's sun, the effects on the sun can be measured from Earth[^]. The fact that the system is in prefect balance looks amazing, but it isn't, the path of one body interacing with
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Dalek Dave wrote:
Firstly it is called tangential velocity.
It's called whatever I bloody well decide to call it, especially in the context of a discussion board, where such frippery is not relevant. Google again, you'll find that there are several ways of describing/naming it.
Dalek Dave wrote:
Second...CONSTANT force would be an acceleration.
I don't see what point you're trying to make, here, but it's wrong, nonetheless. If a constant force is used to overcome friction, there's no acceleration.
Dalek Dave wrote:
All it needs is a single force applied once to give the required velocity, conservation of angular momentum and basic physics mean that once orbit is achieved, no further force is necessary.
Bollocks. If there's any friction at all, the angular momentum is affected, and not even the remotest parts of space contain an absolute vacuum.
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As explained elsewhere, the dissolution of the orbit would occur over such a time frame that other factors would be greater. qv by the time the moon has moved sufficiently far from the earth for the gravitation to be negligible, the sun would be a brown dwarf.
Mark_Wallace wrote:
If a constant force is used to overcome friction, there's no acceleration
If we are talking Maths here that that is irrelevant, and even in the real universe it would be such a small amount as to be safely ignored. When you consider how long the universe has been around, the friction of matter in the otherwise vacuum of space doesn't amount to a hill of beans. I would be more concerned with the effects of relativity rather than the tiny perceived friction of particles. Also, there is no such thing as a vacuum, as a vacuum would not contain energy or gravity or time, and it has to have somewhere to 'be'. This level of conceptual physics is probably beyond most people here, and I certainly do not understand the concept of non-spacetime volumes within a multi-dimensional universe. It is entirely probably that we do not live in a Minkowski universe, it is just that assuming we do makes the maths easier.
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]
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My dilemma today is why do things orbit other things - moons, planets, satellites, that sort of thing. If something in orbit around the earth gets too close it falls to the ground/burns up etc. Too far away and the thing will just keep going under its own momentum and disappear into space. So, there must be an exact distance where these two opposing concepts balance themselves out and things orbit happily. But for that to work, everything would have to be exact, which it isn't. Maybe orbits are just transitory things which happen for a bit but they're the only things we can see. If everything just drifted all over the place in space there wouldn't really be any structure. What's going on?
Regards, Rob Philpott.
What I find amazing is a demonstration of gravity being a weak force: Take a table tennis ball and suspend it from a string. Then take a ruler and get some static electricity into the ruler by rubbing it - the ruler will attract the suspended table tennis ball. If however you take a ten tonne block of steel and place it next to the suspended table tennis ball - the ball will not move. It's the simple things that entertain me :)
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
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Rob Philpott wrote:
But for that to work, everything would have to be exact, which it isn't.
It is [almost] the moon is actually spiralling out (about 1cm a year IIRC, a fact on discovered when NASA put mirrors on the moon so we could more accurately measure distance using LASERs. Which is beyond freakin' cool). The basic principle fo a circular orbit is as DD describes: The moon is being pulled (accelerated) towards the Earth, but it's momentum is at 90°, the accelration changes the velocity (the direction component, not the speed) continually in this way so the moon follows a circular path. The situation is slightly more complicated inm reality: the orbit is an elipse (so the momentum isn't always 90° and the speed of the moon slows down and speeds up depending where in the orbit it is. For a real mind-bendy situation, the moon and the Earth both orbit their combined centre of gravity[^], so the earth will appear to wobble when viewed from a distance: the same thing happens when a planet orbits it's sun, the effects on the sun can be measured from Earth[^]. The fact that the system is in prefect balance looks amazing, but it isn't, the path of one body interacing with
Keith Barrow wrote:
Additionally there is a theory (now favoured I think) that the Moon is actually a part of the Earth that broke of early in our history when something large smashed into the proto-Earth, so the moon was flung out into orbit rather than fell in
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]
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What I find amazing is a demonstration of gravity being a weak force: Take a table tennis ball and suspend it from a string. Then take a ruler and get some static electricity into the ruler by rubbing it - the ruler will attract the suspended table tennis ball. If however you take a ten tonne block of steel and place it next to the suspended table tennis ball - the ball will not move. It's the simple things that entertain me :)
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
GuyThiebaut wrote:
If however you take a ten tonne block of steel and place it next to the suspended table tennis ball - the ball will not move.
It will, but to such a small degree that you will not see it. There are satellites that measure the gravitational fields of different parts of the earth from orbit, and whilst 10 tons is not a lot, a small hill here or a large city there do show up as having gravity measurable over the earth norm. It is pretty impressive really.
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^]
