What keeps the moon from crashing into the Earth?

[George P Burdell]

Originally posted by: dullard

Originally posted by: MIKEMIKE
The fictitious centrifugal force appears when a rotating reference frame is used for analyzing the system. The centrifugal force is exerted on all objects, and directed away from the axis of rotation.

I guess you didn't see the wink.

Centrifugal forces do exist. Just not in planetary motion.

 

[SagaLore]

Isn't the word you guys are looking for, centripetal force?

 

[TheStu]

look at it this way...

Stand on top of mount everest and level everything else lower than the peak... so it becomes a nice triangular mountain... now take a ball and throw it as hard as you can... the flight path of the ball is straight for a while and then falls right? Now haul up a cannon and shoot the same ball out of it... the flight path is straight again and farther this time before it falls to the earth... now, haul up a rocket engine for the ball and launch so that the straight part of the flight path takes it out of the atmosphere, now let the ball fall... it will fall straight down, but the earth's gravity will pull it back in, correcting its path


The moon is much the same, it actually <i>is</i> falling toward teh earth, but it is also moving forward in relation to the earth, so the earth's gravity is there to keep the orbit of the moon consistent... the moon doesnt crash into the earth because it is falling past it (you sort of have to think of this in 2D)

 

[plastick]

That link for the planetary orbits is perfect. its one of the right pieces i need to form my understanding

 

[dullard]

Originally posted by: George P Burdell
Centrifugal forces do exist. Just not in planetary motion.

Again, I'm showing the silliness of his spelling nazi ways.

 

[plastick]

Originally posted by: TheStu
look at it this way...

Stand on top of mount everest and level everything else lower than the peak... so it becomes a nice triangular mountain... now take a ball and throw it as hard as you can... the flight path of the ball is straight for a while and then falls right? Now haul up a cannon and shoot the same ball out of it... the flight path is straight again and farther this time before it falls to the earth... now, haul up a rocket engine for the ball and launch so that the straight part of the flight path takes it out of the atmosphere, now let the ball fall... it will fall straight down, but the earth's gravity will pull it back in, correcting its path


The moon is much the same, it actually <i>is</i> falling toward teh earth, but it is also moving forward in relation to the earth, so the earth's gravity is there to keep the orbit of the moon consistent... the moon doesnt crash into the earth because it is falling past it (you sort of have to think of this in 2D)

falling past it.... thats kind of what i was thinking.. its constantly missing it because of... see i need more understanding though.

thanks for your help

 

[DaShen]

Originally posted by: Descartes
It has to do with its orbital velocity. It's sufficient enough to keep the moon from crashing into earth through gravitational decay, and as someone else said it's actually enough such that the moon is receding in its orbit slightly every year.

Yes.

Although, CrackRabbit, I thought that the moon was slowly entering the Earth's Orbit? Not the other way around. Hmmm, I will have to check up on that.

I think they hypothesize that it is an offshoot of Earth, when a large meteor hit it. At the time of the Moon creation, I know that they say that the moon was much closer to the earth and caused enormous gravitational pull which created large mountanous regions, so you could be right that the Moon is slowly traveling away from the Earth, but that would be a larger velocity than orbital velocity and possible dark matter.

 

[George P Burdell]

This will work only on Mozilla:
How Did The Moon Get Into Orbit?

 

[ahurtt]

In the most basic sense of an explanation, motion is what keeps the moon from crashing into the earth.

 

[Mo0o]

The ball has a tangential velocity to the surface of the earth with a constant force inwards. In essen it's constantly falling into the earth but since its traveling trangentially as well, it maintains an geosynchronous orbit.

 

[plastick]

Originally posted by: ahurtt
In the most basic sense of an explanation, motion is what keeps the moon from crashing into the earth.

and the most basic explination of what holds every relative thing together is that of absolute God. But that doesnt tell me anything...

 

[plastick]

Originally posted by: Mo0o
The ball has a tangential velocity to the surface of the earth with a constant force inwards. In essen it's constantly falling into the earth but since its traveling trangentially as well, it maintains an geosynchronous orbit.

okay its making more sence now...


btw: nice sig to have... ROFDL

 

[Descartes]

Originally posted by: Mo0o
The ball has a tangential velocity to the surface of the earth with a constant force inwards. In essen it's constantly falling into the earth but since its traveling trangentially as well, it maintains an geosynchronous orbit.

No body can maintain orbit indefinitely, I believe. There are fairly stable points referred to as Lagrange Points, but those too are only stable over a period relative to the body's masses, velocity, etc. Eventually a body will succomb to one of two things: Decay in the form of gravitational or, in the case of earth, atmospheric; An increase in orbital velocity from some influence (another planet perhaps, an Aristotelian angle pushing it around, etc.) that exceeds its escape velocity and thus pushes it beyond its orbit.

 

[Mo0o]

Originally posted by: plastick

Originally posted by: Mo0o
The ball has a tangential velocity to the surface of the earth with a constant force inwards. In essen it's constantly falling into the earth but since its traveling trangentially as well, it maintains an geosynchronous orbit.

okay its making more sence now...


btw: nice sig to have... ROFL

Just think of it this way. A ball is traveling tangentially to the earth. Every time it moves an inch, gravity pulls it into the earth a little. But then it travels tangentially again so it gets furthur out from earth once again. Then gravity pulls it back in to where it was before, in terms of its distance from the earth. Granted the motion is not discrete(is that teh word?) like that, that's a picture you should have in your head. So basically if gravity was to stop, the moon would shoot off into space in a tangential vector to its position to the earth at teh time gravity stopped

 

[Mo0o]

Originally posted by: Descartes

Originally posted by: Mo0o
The ball has a tangential velocity to the surface of the earth with a constant force inwards. In essen it's constantly falling into the earth but since its traveling trangentially as well, it maintains an geosynchronous orbit.

No body can maintain orbit indefinitely, I believe. There are fairly stable points referred to as Lagrange Points, but those too are only stable over a period relative to the body's masses, velocity, etc. Eventually a body will succomb to one of two things: Decay in the form of gravitational or, in the case of earth, atmospheric; An increase in orbital velocity from some influence (another planet perhaps, an Aristotelian angle pushing it around, etc.) that exceeds its escape velocity and thus pushes it beyond its orbit.

Right, I just ignored orbital decay since it's not really an important factor to consider if he just wants to know how orbits work. No sense cluttering a simple explanation of orbits with Lagrange

 

[Ausm]

Physics my friend...


/Thread


Ausm

 

[Metron]

Try here... PBS Series on the Elegant Universe.

 

[plastick]

Originally posted by: Mo0o

Originally posted by: plastick

Originally posted by: Mo0o
The ball has a tangential velocity to the surface of the earth with a constant force inwards. In essen it's constantly falling into the earth but since its traveling trangentially as well, it maintains an geosynchronous orbit.

okay its making more sence now...


btw: nice sig to have... ROFL

Just think of it this way. A ball is traveling tangentially to the earth. Every time it moves an inch, gravity pulls it into the earth a little. But then it travels tangentially again so it gets furthur out from earth once again. Then gravity pulls it back in to where it was before, in terms of its distance from the earth. Granted the motion is not discrete(is that teh word?) like that, that's a picture you should have in your head. So basically if gravity was to stop, the moon would shoot off into space in a tangential vector to its position to the earth at teh time gravity stopped

yeah i get it now... both forces are in effect continuously at the same time and there is a "sloped" result. That result is dependant on those and other variables.. certian variables are what i was trying to understand ...etc

thanks

 

[Armitage]

Originally posted by: Mo0o
The ball has a tangential velocity to the surface of the earth with a constant force inwards. In essen it's constantly falling into the earth but since its traveling trangentially as well, it maintains an geosynchronous orbit.

A geosynchronous orbit is a particular class of orbit that is (nearly) circular and has a period equal to the rotation period of the earth (24 hours). If the inclination is 0 as well it will also be geostationary in addition to being geosyncronous. The end effect is that the satellite will appear to be stationary in the sky as seen from earth.

 

[Armitage]

Originally posted by: Mo0o

Originally posted by: plastick

Originally posted by: Mo0o
The ball has a tangential velocity to the surface of the earth with a constant force inwards. In essen it's constantly falling into the earth but since its traveling trangentially as well, it maintains an geosynchronous orbit.

okay its making more sence now...


btw: nice sig to have... ROFL

Just think of it this way. A ball is traveling tangentially to the earth. Every time it moves an inch, gravity pulls it into the earth a little. But then it travels tangentially again so it gets furthur out from earth once again. Then gravity pulls it back in to where it was before, in terms of its distance from the earth. Granted the motion is not discrete(is that teh word?) like that, that's a picture you should have in your head. So basically if gravity was to stop, the moon would shoot off into space in a tangential vector to its position to the earth at teh time gravity stopped

:thumbsup:

 

[Armitage]

Originally posted by: Descartes

Originally posted by: Mo0o
The ball has a tangential velocity to the surface of the earth with a constant force inwards. In essen it's constantly falling into the earth but since its traveling trangentially as well, it maintains an geosynchronous orbit.

No body can maintain orbit indefinitely, I believe. There are fairly stable points referred to as Lagrange Points, but those too are only stable over a period relative to the body's masses, velocity, etc. Eventually a body will succomb to one of two things: Decay in the form of gravitational or, in the case of earth, atmospheric; An increase in orbital velocity from some influence (another planet perhaps, an Aristotelian angle pushing it around, etc.) that exceeds its escape velocity and thus pushes it beyond its orbit.

Not really - if you are out of the drag regime (say perigee about 10000 Km altitude) but still in an orbit where the earth is the primary gravitational influence by a large factor, the object will remain in orbit essentially forever. The shape and orientation will change due to various perturbative factors (3rd body, earth geopotential, solar radiation pressure, etc.). But it won't decay or escape.

 

[Descartes]

Originally posted by: Armitage

Originally posted by: Descartes

Originally posted by: Mo0o
The ball has a tangential velocity to the surface of the earth with a constant force inwards. In essen it's constantly falling into the earth but since its traveling trangentially as well, it maintains an geosynchronous orbit.

No body can maintain orbit indefinitely, I believe. There are fairly stable points referred to as Lagrange Points, but those too are only stable over a period relative to the body's masses, velocity, etc. Eventually a body will succomb to one of two things: Decay in the form of gravitational or, in the case of earth, atmospheric; An increase in orbital velocity from some influence (another planet perhaps, an Aristotelian angle pushing it around, etc.) that exceeds its escape velocity and thus pushes it beyond its orbit.

Not really - if you are out of the drag regime (say perigee about 10000 Km altitude) but still in an orbit where the earth is the primary gravitational influence by a large factor, the object will remain in orbit essentially forever. The shape and orientation will change due to various perturbative factors (3rd body, earth geopotential, solar radiation pressure, etc.). But it won't decay or escape.

What I was arguing was the idea of "essentially"; essentially by what timeframe? I'm merely pointing out that over a sufficient timeframe nothing remains forever; hence my use of the word indefinitely...

 

[whistleclient]

Fear.

 

[Descartes]

Originally posted by: Armitage

Originally posted by: Mo0o
The ball has a tangential velocity to the surface of the earth with a constant force inwards. In essen it's constantly falling into the earth but since its traveling trangentially as well, it maintains an geosynchronous orbit.

A geosynchronous orbit is a particular class of orbit that is (nearly) circular and has a period equal to the rotation period of the earth (24 hours). If the inclination is 0 as well it will also be geostationary in addition to being geosyncronous. The end effect is that the satellite will appear to be stationary in the sky as seen from earth.

Are you sure the moon is geosynchronous? If so, how do we have tides? Perhaps you're instead referring to gravitional locking?

 

[spidey07]

IIRC, orbit is really nothing more than perpetually falling.

that whole gravity thing.