The Moon

[Jehosefat]

The centripetal force is the force exerted by the string/arm/gravity on the ball/bucket/moon that stops it from flying off away from the centre of the orbit.

Satellites don't need to have rocket fuel to keep orbiting the earth necessarily. They are specifically put into decaying orbits so that they will fall out of orbit and burn up when their usefulness is finished rather than cluttering up orbits that could be used for a new satellite.

 

[Mars]

The centripetal force is the force exerted by the string/arm/gravity on the ball/bucket/moon that stops it from flying off away from the centre of the orbit.

Satellites don't need to have rocket fuel to keep orbiting the earth necessarily. They are specifically put into decaying orbits so that they will fall out of orbit and burn up when their usefulness is finished rather than cluttering up orbits that could be used for a new satellite.

What CAUSES the force in reference to gravity in planets and planetoids. Do we not know how gravity works? or rather not how, but why. I'm guessing it has something to do with mass, but I honestly have no idea.

If you where to build a gravity field generator, what would need to happen in order for there to be a downward pulling force strong enough to keep your feet under you.

 

[dabean]

Do we not know how gravity works?

No we don't. That why they build things like the Large Hadron Collider to figure out what gives mass to some things and not others.

Until we figure that out there'll be no gravity field generators.

 

[Naks]

The moon is actually moving away.

Yep. This is why in early historial depictions, the moon is drawn much bigger than it is today. more info: http://curious.astro.cornell.edu/question.php?number=124

 

[AlphaJohn]

The moon is actually moving away.

Nope its falling towards earth that is why its rotating... it keeps on "missing" it. The only way it would move away is if it gained enery ad for that it needs some sort of rocket. For now its losing energy and thus moving closer but like I said this loss is minimal so it doesn't happen all at once.

Ok, I have now learned about Centripetal force.
What causes it tho? Centrifugal force is caused by the momentum involved in the energy used in pushing it away, and the string on the ball or the arm on the bucket keeps it from flying away.

What is the energy that causes Centripetal force?

Centripetal as in planets/moon and the sun is cause by gravity, the energy source is caused by the attraction the bodies of mass exert onto each other.
Centrifugal as in the bucket of water is accelaration cause by the arm spinning it, or in case of space ships the huge ass rockets that helps it overcome the force exerted by gravity. ie: External.

What CAUSES the force in reference to gravity in planets and planetoids. Do we not know how gravity works? or rather not how, but why. I'm guessing it has something to do with mass, but I honestly have no idea.

If you where to build a gravity field generator, what would need to happen in order for there to be a downward pulling force strong enough to keep your feet under you.

Now we getting a bit deeper, Best way to explain it is ala Einstein's example like placing objects onto a rubber band, the heavier(More mass) they have the deeper the dent in the rubber(gravity) this dent makes thing that is lighter move towards the massive object. Oh and what causes particles to have mass is the ultimate question. Hence the LHC search for the higgs boson.

 

[AlphaJohn]

Satellites don't need to have rocket fuel to keep orbiting the earth necessarily. They are specifically put into decaying orbits so that they will fall out of orbit and burn up when their usefulness is finished rather than cluttering up orbits that could be used for a new satellite.

Sure not all of them have rockets. Esp the cheaper once. But go read up and you will see that the bigger ones do. Also goes for the space station:

http://idiotsguides.com/static/quic...how-does-the-space-station-stay-in-orbit.html is a good read on this.

 

[Mars]

No we don't. That why they build things like the Large Hadron Collider to figure out what gives mass to some things and not others.

Until we figure that out there'll be no gravity field generators.

Thank you, until now whenever I ask the question I get either an explanation on how gravity works (when you drop it, it falls down see? ) or I get the centrifugal explanation.

 

[Maverick Jester]

Until we figure that out there'll be no gravity field generators.

Such a shame...

 

[Mars]

Nope its falling towards earth that is why its rotating... it keeps on "missing" it. The only way it would move away is if it gained enery ad for that it needs some sort of rocket. For now its losing energy and thus moving closer but like I said this loss is minimal so it doesn't happen all at once.



Centripetal as in planets/moon and the sun is cause by gravity, the energy source is caused by the attraction the bodies of mass exert onto each other.
Centrifugal as in the bucket of water is accelaration cause by the arm spinning it, or in case of space ships the huge ass rockets that helps it overcome the force exerted by gravity. ie: External.



Now we getting a bit deeper, Best way to explain it is ala Einstein's example like placing objects onto a rubber band, the heavier(More mass) they have the deeper the dent in the rubber(gravity) this dent makes thing that is lighter move towards the massive object. Oh and what causes particles to have mass is the ultimate question. Hence the LHC search for the higgs boson.

But our mass is in relation to the planet surely? Or if I where floating in space, would I also have a very small gravitational field?

 

[AlphaJohn]

But our mass is in relation to the planet surely? Or if I where floating in space, would I also have a very small gravitational field?

You have gravity where-ever you are, thing is here on earth, this big thing under our feet trumps ours so its attraction is stronger than ours. So yes in empty space you might see it better if you have something small like a ball + and enough time, you will attract it.

So simply put everything with mass has a gravitational attraction.

See:

[video=youtube;p_o4aY7xkXg]http://www.youtube.com/watch?v=p_o4aY7xkXg[/video]

Ooh found a better one: http://www.youtube.com/watch?v=0rocNtnD-yI

 

[Mars]

Ok I got it.

did you guys learn this stuff at school? I knew being stoned at school was going to bite me in the ass sooner or later.

 

[AlphaJohn]

did you guys learn this stuff at school? I knew being stoned at school was going to bite me in the ass sooner or later.

Yep, Sciece 101

Now that you got General Relativity can we start with the true brain smasher.... quantum mechanics, ie the part of physics that goes F U to general relativity.

 

[Mars]

Yep, Sciece 101

Now that you got General Relativity can we start with the true brain smasher.... quantum mechanics, ie the part of physics that goes F U to general relativity.

It amazes me how I got through school! I vaguely remember something about waves and particles being together in regard to quantum mechanics.

 

[AlphaJohn]

It amazes me how I got through school! I vaguely remember something about waves and particles being together in regard to quantum mechanics.

Aaah you talking about the wave–particle duality, that's a can of worms if I ever seen one. Just bloody glad it only works in the micro.

Well to be honest do not ask me anything I learned in history, geography or even accounting, I would be in the same boat as you, but science and math/geometry now that was the subjects I actually liked.

 

[Maverick Jester]

Yep, Sciece 101

Now that you got General Relativity can we start with the true brain smasher.... quantum mechanics, ie the part of physics that goes F U to general relativity.

Quantum mechanics is fun...

 

[AlphaJohn]

Quantum mechanics is fun...

Not for the cat, it isn't

 

[Jehosefat]

@AlphaJohn: By moving away, he meant that the moon's orbital "radius" is increasing. And no, it does not need to gain energy to do this. Any orbit can either decay, remain steady or explode and it all depends on what the initial parameters are. For a given mass and "radius" there is a single orbital velocity that describes the steady state orbit (assuming that "radius" means orbital shape). Any velocity below this and the orbit will decay, any velocity above this and the orbit will explode. How quickly the orbit changes depends on how different the velocity is from the steady state velocity.

I never said that satellites don't need rocket boosters, there are many practical considerations as to why they do (station-keeping, re-aiming, collision avoidance etc.), but from a purely orbital standpoint, they do not necessarily need rockets to remain in orbit. They have been designed and specifically placed in decaying orbits so that they will eventually fall back to earth and burn up in the atmosphere to keep the limited number of useful orbits clear of obsolete satellites that would pose a collision risk to the sparkly new ones.

 

[AlphaJohn]

@AlphaJohn: By moving away, he meant that the moon's orbital "radius" is increasing. And no, it does not need to gain energy to do this. Any orbit can either decay, remain steady or explode and it all depends on what the initial parameters are. For a given mass and "radius" there is a single orbital velocity that describes the steady state orbit (assuming that "radius" means orbital shape). Any velocity below this and the orbit will decay, any velocity above this and the orbit will explode. How quickly the orbit changes depends on how different the velocity is from the steady state velocity.

Erm no.... just no.

The Moon, at first, will recede further and further from the Earth, but the two bodies will continue to orbit about their common centre of gravity. Around 600,000,000 years from now, the Moon will be too far away for total eclipses to occur.

However, this process won't continue indefinitely

Once the Earth becomes tidally locked with the Moon, the solar tides will tend to slow the Earth’s rotation even more, so the day will be longer than the month and the Moon will rise in the West and set in the East. The water spheroid generated by the Sun will cause the high tide to appear earlier than the time of highest moon ... Then the tidal force of Earth on the Moon will pull the Moon into a lower orbit and eventually inside the Roche limit (18500 km), whereupon the Moon will disintegrate producing a ring round the Earth.

Source: http://outreach.physics.utah.edu/labs/tides/tides_new2.pdf

So yes for now they moving apart but thats because of external energy added by the wobble (Must admit forgot about that) but when the added energy is no more its gonna come toward us.

I never said that satellites don't need rocket boosters, there are many practical considerations as to why they do (station-keeping, re-aiming, collision avoidance etc.), but from a purely orbital standpoint, they do not necessarily need rockets to remain in orbit. They have been designed and specifically placed in decaying orbits so that they will eventually fall back to earth and burn up in the atmosphere to keep the limited number of useful orbits clear of obsolete satellites that would pose a collision risk to the sparkly new ones.

From the link I gave you

If some force were to slow the forward motion of the space station, gravity would pull it to Earth. Satellite orbits must be located above the atmosphere. Otherwise, the force of friction with the air would slow the satellite, causing it to fall. If the force of gravity were suddenly to disappear, the space station would head away in a straight line.

In fact, the space station does not hold a perfect orbit. There is some atmospheric friction, even though the atmosphere is very thin at its altitude, so it tends to lose about a mile and a half of altitude every month. When it reaches a lower altitude limit, the station is pushed several miles higher by a rocket or space shuttle.

Also See https://engineering.purdue.edu/~propulsi/propulsion/rockets/satellites.html

A satellite or spacecraft orbiting the earth or traveling through the solar system encounters very small forces. For this reason, many satellite propulsion systems must deliver very precise ``impulse bits'' in order to accurately control the position or attitude of these objects. Reliability is of utmost importance in these systems since there is normally no real opportunity to service them over their entire lifetime. High performance is also a must; higher Isp systems provide additional on-orbit lifetime or the capability to increase the ``payload'' portion of the spacecraft. Traditionally, chemical propulsion systems using monopropellant (single fluid) or bipropellant (two fluid) liquid thrusters have been employed for these applications. However, the growth in spacecraft power has led to the use of higher energy electric propulsion (EP) systems for many modern missions. Arcjet thrusters heat a working fluid such as ammonia gas to very high temperatures by flowing the gas through a spark between two closely-spaced electrodes. More recently, ion thrusters have seen service on commercial spacecraft. These thrusters operate by accelerating heavy ions created in a plasma inside the device. Hall effect thrusters work on similar principles; these devices are the focus of many current studies.

They have a whole list of rockets em satellites have.

 

[Joe_Soap]

Common misunderstanding I hear from some people during discussions about gravity.

My favourite one is: "If the earth or core stops spinning we'll fall off"

???

Apparently the moon slows down the spinning of the earth. So if there is not moon, earths rotation will increase in speed.

 

[Jehosefat]

Erm no.... just no.

Didn't understand a word I said did you?

Source: http://outreach.physics.utah.edu/labs/tides/tides_new2.pdf

So yes for now they moving apart but thats because of external energy added by the wobble (Must admit forgot about that) but when the added energy is no more its gonna come toward us.

Its a closed system. By definition the "wobble" can't add any energy to the system because it is part of it. So no energy being added and the moon is moving further away. So while yes, eventually the moon will get closer to the earth, it has absolutely nothing to do with the reason that you gave in your earlier post.

Also See https://engineering.purdue.edu/~propulsi/propulsion/rockets/satellites.html

They have a whole list of rockets em satellites have.

Again you completely missed what I was saying. Yes, the ISS does drop towards earth because there is a non-negligible amount of friction due to the fact that it is in low earth orbit. For satellites that are in high earth orbit this friction is almost negligible however there are, of course, other forces acting on them. At no point did I say that they do not need rockets, all I said was that the necessity of the rockets was largely due to external factors rather than a necessary function of something being in an orbit.