Influence of Earth's Gravitational pull

davyjose

At what point does the earth's gravitational pull cease? What I mean is, how high can you go before you would reach the limit of where you would fall back to earth. Presumably, this would vary given the object's mass, but any rough ideas?

Another question, if the moon is in the earth's gravitational pull, how come they don't collide? Is this down to atmosphere, or the fact that they're both spinning fast, or what?

Just Curious,

Dave

Spear

davyjose wrote: »

At what point does the earth's gravitational pull cease? What I mean is, how high can you go before you would reach the limit of where you would fall back to earth. Presumably, this would vary given the object's mass, but any rough ideas?

Escape velocity depends upon the mass of the body being escaped from, not the mass of the escaping body.

http://en.wikipedia.org/wiki/Escape_velocity

Another question, if the moon is in the earth's gravitational pull, how come they don't collide? Is this down to atmosphere, or the fact that they're both spinning fast, or what?

Just Curious,

Dave

The earth and moon orbit each other centred upon their barycenre point.

http://en.wikipedia.org/wiki/Barycentre#Barycenter_in_astronomy

AtomicHorror

davyjose wrote: »

Another question, if the moon is in the earth's gravitational pull, how come they don't collide? Is this down to atmosphere, or the fact that they're both spinning fast, or what?

Orbits work because of gravity. Essentially the moon is falling towards the Earth, but missing. As long as an object's angular velocity is sufficient, it'll fall around a larger mass rather than collide. To a lesser extent, the Earth is also being pulled towards the moon.

Pgibson

The Earth's gravitational reach has no limit.It extends to the ends of the Universe.

The reason the Andromeda Galaxy and the Milky way are approaching each other is because EVERY SINGLE ATOM in both galaxies is tugging on the other's atoms.

The gravitational pull of your own body is contributing to the approach of the Andromeda Galaxy.

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davyjose

Pgibson wrote: »

The Earth's gravitational reach has no limit.It extends to the ends of the Universe.

Yeah I was aware of this. To be honest I can see it was a naive question. I basically meant at what point would you start floating away into space rather than falling back to earth, but further research has made me see that it's a little bit more complicated than that.

Thanks for the replies guys.

Michael Collins

davyjose wrote: »

...Another question, if the moon is in the earth's gravitational pull, how come they don't collide? Is this down to atmosphere, or the fact that they're both spinning fast, or what?...

As AtomicHorror says the moon is "falling" towards earth all the time. If you know about Newton's Laws you'll know that things that are moving want to remain travelling in a straight line. The force of attraction between the Moon and the Earth cause an acceleration (a change in direction) of the Moon, making it orbit the earth, otherwise it would fly off into space at a tanget to its orbit. The moon is in fact spiralling into the earth (or vice versa!) since the kinetic energy of the moon is falling all the time when it bumps into particles etc. It is, of course, happing very slowly...

Captain Chaos

I thought the Moon is slowly breaking away from the Earth as it is getting further and further away with time very, very slowly. My understanding is that it used to orbit much closer hundreds of thousands of years ago, or where ever I read that was completely wrong?.

bennyblanco

Isnt the gravity well thing part of it?:pac:or am I reading too much sci fi?

Michael Collins

Captain Chaos wrote: »

I thought the Moon is slowly breaking away from the Earth as it is getting further and further away with time very, very slowly. My understanding is that it used to orbit much closer hundreds of thousands of years ago, or where ever I read that was completely wrong?.

Yep, you are right here. I was thinking of the earth (which is actually slowing down on its orbit around the sun). In fact the moon is taking some of the earth's energy - hence it is in fact, speeding up! Hence it is moving to a higher orbit all the time...

Pgibson

davyjose wrote: »

I basically meant at what point would you start floating away into space rather than falling back to earth.

You will ALWAYS be falling towards the earth unless your velocity AWAY from the earth is at or above "Escape Velocity".(11.2 km per second on surface)

If you could jump off the surface of the earth at 11.2 km per second the gravity of earth will forever be slowing you down..but at that speed you will be at "infinity" before you stop and start to "fall back".

Above that speed you will never be "decelerated" to a halt. Just like the Pioneer and Voyager Spacecraft before you, you will have escaped the clutches of the earth forever.

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ronbyrne2005

Cant gravity become or be made a repulsive force over large distances thru dark matter/energy? Heard some cosmologist on rte the other day talking about it but did'nt fully hear what he was saying.

Pgibson

That was Prof Michael Rowan-Robinson.

You can buy a DVD of the lecture he gave last Monday here:

http://www.astronomy.ie/lecture200808.html

As for the acceleration which seems to occur at cosmological distances,
That is at the sharp cutting edge of "the known".

Strange creatures like "Dark Energy" have to be invoked..but no one knows what is really going on yet.

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