A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Others » Misc
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Q. Trying to understand concept in gravity



 
 
Thread Tools Display Modes
  #1  
Old July 29th 03, 02:38 AM
Jim Jones
external usenet poster
 
Posts: n/a
Default Q. Trying to understand concept in gravity

Hi.

If it where possible to create or to send 2 incredibly huge boulders
into outer space from Earth and just let them float out there , would
they eventually revolve around each other ? Is that how masses in
outer space work? They just find their gravitation point, and start to
"do si do" ?

What if launched from the moon ?

Or, would our solar system reject them? If so, what would it do with
these 2 new intruders, which did not come from way out there, but from
our modest little planet ?
Would they hook up with the asteroid belt outside of mars ?

Would they stay together at all, if when on earth they had absolutely
no magnetic properties ?

Does the pull of gravity get stronger on larger planets and weaker on
smaller planets ?

Why do the planets and moons pull (gravity) anyway? Is it because
they're so large? Is it the activity at the core?

Thanks in advance,

Jim




  #2  
Old July 29th 03, 11:01 AM
Ron Miller
external usenet poster
 
Posts: n/a
Default Q. Trying to understand concept in gravity


"Jim Jones" wrote in message
...
Hi.

If it where possible to create or to send 2 incredibly huge boulders
into outer space from Earth and just let them float out there , would
they eventually revolve around each other ? Is that how masses in
outer space work? They just find their gravitation point, and start to
"do si do" ?


More or less, yes.

What if launched from the moon ?


Would make no difference.

Or, would our solar system reject them? If so, what would it do with
these 2 new intruders, which did not come from way out there, but from
our modest little planet ?


The solar system could care less.

Would they hook up with the asteroid belt outside of mars ?


Not necessarily. They would orbit wherever you launched them to.

Would they stay together at all, if when on earth they had absolutely
no magnetic properties ?


Gravity is the operator here, not magnetism.

Does the pull of gravity get stronger on larger planets and weaker on
smaller planets ?


Yes.

Why do the planets and moons pull (gravity) anyway? Is it because
they're so large? Is it the activity at the core?


It is because of their mass.

RM


  #3  
Old July 30th 03, 01:27 AM
Jim
external usenet poster
 
Posts: n/a
Default Q. Trying to understand concept in gravity

On Tue, 29 Jul 2003 06:01:14 -0400, "Ron Miller"
wrote:


"Jim Jones" wrote in message
.. .
Hi.

If it where possible to create or to send 2 incredibly huge boulders
into outer space from Earth and just let them float out there , would
they eventually revolve around each other ? Is that how masses in
outer space work? They just find their gravitation point, and start to
"do si do" ?


More or less, yes.

What if launched from the moon ?


Would make no difference.

Or, would our solar system reject them? If so, what would it do with
these 2 new intruders, which did not come from way out there, but from
our modest little planet ?


The solar system could care less.

Would they hook up with the asteroid belt outside of mars ?


Not necessarily. They would orbit wherever you launched them to.

Would they stay together at all, if when on earth they had absolutely
no magnetic properties ?


Gravity is the operator here, not magnetism.

Does the pull of gravity get stronger on larger planets and weaker on
smaller planets ?


Yes.

Why do the planets and moons pull (gravity) anyway? Is it because
they're so large? Is it the activity at the core?


It is because of their mass.

RM


Ron,

Thanks for your prompt response and your help in clearing up those
things, but I may be unclear on what you mean, in the last statement,
about "It's their mass".

Let me rephrase my question. And please don't think you're being too
simple in answering:
Q. Why does earth hang onto it's loose objects ? What about "mass"
might I not be understanding.

ALSO: Does gravity gradually drop off, as we get higher and higher
into the atmosphere, OR, is there a fine line where gravity goes from
gravity to no gravity?

Thanks again,
Jim

  #4  
Old July 30th 03, 02:28 AM
Bill Nunnelee
external usenet poster
 
Posts: n/a
Default Q. Trying to understand concept in gravity

Let me correct the equation before somebody else does. :-)

F = (G * m1 * m2) / r^2

Where G is the gravitational constant.


"Bill Nunnelee" wrote in message
thlink.net...
The outcome of the boulders would depend on their velocities relative to
each other. If zero (and they were sufficiently close to each other),

their
mutual gravitational attraction would pull them together---instead of
orbiting, they would collide. (Gravity works over any distance, but if

they
were too far apart, the influence of other solar system bodies would
probably overwhelm any mutual attraction.) It wouldn't matter if they

were
launched from the earth or the moon.

Whether they would stay or go depends on whether they were given enough of
an initial push to reach escape velocity or not. The initial speed and
direction would also determine their orbit around the sun if they stayed.
They could also be ejected by passing close to another body and picking up
some of the body's energy. Gravitational assists were used with many

space
probes, and close passages of Jupiter have been responsible for ejecting
many comets over time.

Magnetism is an entirely different force. The strength of gravity depends
on the mass of the two objects involved and the distance between them.
Newton expressed it as F = m1*m2 / r^2, where m1 and m2 are the two masses
and r is the distance between them.




"Jim Jones" wrote in message
...
Hi.

If it where possible to create or to send 2 incredibly huge boulders
into outer space from Earth and just let them float out there , would
they eventually revolve around each other ? Is that how masses in
outer space work? They just find their gravitation point, and start to
"do si do" ?

What if launched from the moon ?

Or, would our solar system reject them? If so, what would it do with
these 2 new intruders, which did not come from way out there, but from
our modest little planet ?
Would they hook up with the asteroid belt outside of mars ?

Would they stay together at all, if when on earth they had absolutely
no magnetic properties ?

Does the pull of gravity get stronger on larger planets and weaker on
smaller planets ?

Why do the planets and moons pull (gravity) anyway? Is it because
they're so large? Is it the activity at the core?

Thanks in advance,

Jim










  #5  
Old July 30th 03, 04:43 AM
Kent
external usenet poster
 
Posts: n/a
Default Q. Trying to understand concept in gravity

Jim wrote:

Thanks for your prompt response and your help in clearing up those
things, but I may be unclear on what you mean, in the last statement,
about "It's their mass".


As an amateur myself I can put it the layman's terms I learned for you.
I hope you and Ron don't mind my jumping in. Mass is what determines an
object's gravity, not its size. Mass is simply the amount of "stuff" in
something. For example: a tennis ball and a tennis ball-sized rock.
The rock has more mass (stuff in it) than the tennis ball. In your hands
the rock weighs more than the ball, since there is more stuff in it for
gravity to draw upon (i.e. it weighs more).

Naturally, on the moon the rock would weigh less than it does on Earth,
and on Jupiter it would weigh more. So mass is the term used to describe
"stuff" astronomically, rather than size or weight, in regards to
gravity. Size only comes into it because there's so much more room for
"stuff" to be in. But that doesn't necessarily mean there *will* be
more "stuff" in the bigger object. So you can see that if Jupiter
(mostly gassy) were the same size as Earth (mostly rock), Earth would
have more mass and therefore more gravity. Same goes for if Earth were
the same size as Jupiter.

Let me rephrase my question. And please don't think you're being too
simple in answering:
Q. Why does earth hang onto it's loose objects ?


Gravity, coupled with the fact the loose objects aren't going fast
enough to break away, nor slow enough to plummet to the ground.

ALSO: Does gravity gradually drop off, as we get higher and higher
into the atmosphere, OR, is there a fine line where gravity goes from
gravity to no gravity?


The first. The "Dropping Off Equation", IIRC, is 1/R(squared). Where R
= radius of the Earth = 4000 miles = surface Gravity, or 1 G.

So if you fly out to 4000 miles *above* the surface = 1/2(squared) =
1/4th the strength of surface Gravity = .25 G's.

At the moon (ignoring its own gravity) = .00028 G's.

At Jupiter (ignoring its own gravity) = .000000000000000002 G's

As you can see, we'll never reach 0. Gravity will just drop off into
really, REALLY small numbers the farther out we go. Hope this helps a
bit.

Cheers,
Kent
  #6  
Old July 30th 03, 05:27 AM
Odysseus
external usenet poster
 
Posts: n/a
Default Q. Trying to understand concept in gravity

Jim wrote:

Let me rephrase my question. And please don't think you're being too
simple in answering:
Q. Why does earth hang onto it's loose objects ? What about "mass"
might I not be understanding.

Every body with mass attracts every other, in proportion to the
masses of both and in inverse proportion to the square of the
distance between their centres. Bill posted this same statement in
the form of an equation. On earth our principal experience of mass is
in the form of weight; a "heavy" object has a large mass, while the
mass of a "light" object is small. The weight of an object measures
the strength of its attraction to the earth, whose mass is so
enormous that it dominates everything near it. We don't notice the
attraction of one 'ordinary-sized' object for another because gravity
is very weak -- except when things as big as planets and moons are
involved. But using extremely sensitive torsion balances, the
gravitational attraction between very large weights suspended very
close to each other can actually be measured in a laboratory.

An object resting on the earth's surface stays where it is because
the ground 'pushes back' with an equal force; if unsupported it will
fall with an acceleration called "g", making its speed constantly
increase by a little under ten metres (about 32 feet) per second
every second. In order to raise an object off the surface one has to
supply a lifting force *greater* than the pull of gravity, i.e. the
object's weight.

ALSO: Does gravity gradually drop off, as we get higher and higher
into the atmosphere, OR, is there a fine line where gravity goes from
gravity to no gravity?

It drops off gradually at first, then faster and faster, but never
disappears altogether. In principle the earth's gravity field goes
out to infinity, and in turn we experience gravitational attraction
from every star in our galaxy and beyond -- but at great distances
the forces become too small to have any noticeable effect. The key
here is the "square" part of the inverse square ratio I mentioned
above: the 'weakening' effect of great distance overcomes the
'strengthening' effect of great mass.

--
Odysseus
  #7  
Old July 30th 03, 02:04 PM
BenignVanilla
external usenet poster
 
Posts: n/a
Default Q. Trying to understand concept in gravity

"Kent" wrote in message
...
snip
At Jupiter (ignoring its own gravity) = .000000000000000002 G's

As you can see, we'll never reach 0. Gravity will just drop off into
really, REALLY small numbers the farther out we go. Hope this helps a
bit.

snip

Is this true? Gravity never quites get to 0? I am having one of those
moments. This is shocking. Can someone expound on this? The concept sounds
very important. How far can we actually measure before we can't "sense" the
field anymore?

BV.


  #8  
Old July 30th 03, 07:36 PM
Bill Sheppard
external usenet poster
 
Posts: n/a
Default Q. Trying to understand concept in gravity

Surely gravity is nullified when an object
equi-distant from two bodies having
equal gravitational pull?


It's called the barycenter (or barycentre to the Brits), the
gravitational null point, or effective center of mass, between two
co-orbiting bodies. In some situations, the barycenter can actually be
below the surface of the larger body.

oc

  #9  
Old July 31st 03, 07:44 AM
Odysseus
external usenet poster
 
Posts: n/a
Default Q. Trying to understand concept in gravity

Jonathan Silverlight wrote:

The forces are still at work. It's like a tug of war, equally balanced
and just as unstable. After all, the moon pulls on the Earth even though
it's well outside the sphere where the Earth dominates (and vice versa).
Of course for other planets the force becomes so small it's
undetectable. I doubt we can detect the pull of Venus, for instance.


It's not too hard to 'ballpark' the numbers: given that Venus has a
mass of about 80% of the earth's, and at inferior conjunction it's
about fifty million kilometres away, nearly eight thousand times the
distance from the earth's centre to the surface. Dividing 0.8 by
8000^2 yields an acceleration value of somewhat over ten billionths
(i.e. 10^-8) of one g -- as you say, pushing the limits of our
ability to detect. By way of comparison the pull of the moon is over
250 times as strong, and that of the sun nearly 50,000 times; another
way to get an idea of our experience of the gravity of Venus might be
to compare it to a ten-tonne weight two metres away.

--
Odysseus
  #10  
Old July 31st 03, 02:58 PM
BenignVanilla
external usenet poster
 
Posts: n/a
Default Q. Trying to understand concept in gravity

"Jonathan Silverlight" wrote in message
...
In message , Andrew McKay
writes
On Wed, 30 Jul 2003 09:04:21 -0400, "BenignVanilla"
wrote:

Is this true? Gravity never quites get to 0? I am having one of those
moments. This is shocking. Can someone expound on this? The concept

sounds
very important. How far can we actually measure before we can't "sense"

the
field anymore?


Surely gravity is nullified when an object equi-distant from two
bodies having equal gravitational pull? In other words it's effect is
additive, suggesting that there is indeed a zero-gravity situation
available.


The forces are still at work. It's like a tug of war, equally balanced
and just as unstable. After all, the moon pulls on the Earth even though
it's well outside the sphere where the Earth dominates (and vice versa).
Of course for other planets the force becomes so small it's
undetectable. I doubt we can detect the pull of Venus, for instance.


So if it's undetectable...is it there? I am seriously asking, not being a
smart ass. I am curious how far out these fields go. I am wondering if some
day distant planets could be found based on some kind of signature.

BV.


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Further proof gravity is a push... Rick Sobie Astronomy Misc 1 March 16th 04 07:20 AM
Debate on GR Jack Sarfatti Astronomy Misc 0 January 9th 04 02:53 AM
Sakharov's Emergent Gravity Jack Sarfatti Astronomy Misc 0 November 17th 03 09:07 PM
Oceanographers Catch First Wave Of Gravity Mission's Success Ron Baalke Science 13 August 7th 03 06:24 AM


All times are GMT +1. The time now is 05:14 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.