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Author Topic:   gravity
shadow71
Member (Idle past 342 days)
Posts: 706
From: Joliet, il, USA
Joined: 08-31-2010


Message 1 of 81 (688072)
01-18-2013 7:08 PM


I am relativity new on the board and was wondering if there have been any threads on the subject of gravity.?

My question is, are there any theories as to How Gravity come into existence?

Was there some evolutionary sequence?

Did it just come into existence with the Big Bang?

Is it natural or metaphysical?

Would appreciate any input from informed people on this board.


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AdminPhat
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Posts: 1792
From: Denver,Colorado USA
Joined: 12-03-2004


Message 2 of 81 (688074)
01-18-2013 8:58 PM


Thread Copied from Proposed New Topics Forum
Thread copied here from the gravity thread in the Proposed New Topics forum.
    
AZPaul3
Member
Posts: 3427
From: Phoenix
Joined: 11-06-2006
Member Rating: 7.4


Message 3 of 81 (688077)
01-18-2013 9:42 PM
Reply to: Message 1 by shadow71
01-18-2013 7:08 PM


Start with some basic research first.

Here

When you have questions outside the most basic come on back. There is a lot of knowledge on the subject in the membership.


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ProtoTypical
Member
Posts: 1702
From: Ontario Canada
Joined: 08-04-2010


Message 4 of 81 (688088)
01-18-2013 11:53 PM
Reply to: Message 3 by AZPaul3
01-18-2013 9:42 PM


Equivalence Principal
From your link

quote:
Gravitation, or gravity, is the natural phenomenon by which physical bodies appear to attract each other with a force proportional to their masses.

and

quote:
Equivalence principle
The equivalence principle, ... expresses the idea that all objects fall in the same way. The simplest way to test the weak equivalence principle is to drop two objects of different masses or compositions in a vacuum, and see if they hit the ground at the same time.

If the attractive force of gravity is proportional to the mass of two bodies, why does an object of greater mass not fall quicker?


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Dr Adequate
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Posts: 15927
Joined: 07-20-2006
Member Rating: 3.8


Message 5 of 81 (688092)
01-19-2013 12:33 AM
Reply to: Message 4 by ProtoTypical
01-18-2013 11:53 PM


Re: Equivalence Principal
If the attractive force of gravity is proportional to the mass of two bodies, why does an object of greater mass not fall quicker?

Because it takes proportionally more force to accelerate a more massive object.

Edited by Dr Adequate, : No reason given.


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AZPaul3
Member
Posts: 3427
From: Phoenix
Joined: 11-06-2006
Member Rating: 7.4


Message 6 of 81 (688095)
01-19-2013 1:11 AM
Reply to: Message 4 by ProtoTypical
01-18-2013 11:53 PM


Re: Equivalence Principal
If the attractive force of gravity is proportional to the mass of two bodies, why does an object of greater mass not fall quicker?

Your talking about two objects falling in earth's gravity well. There is a third body in there: the earth.

Each dropped object is in free fall within earths gravity well. Each object will drop with the same acceleration. That is the Acceleration of Gravity.

The proportional mass part comes in from the mass of object 1 (an apple) vis-a-vis the earth, totally independent of the mass of the other dropped object (a sledge hammer). Both exert an attractive force on the other but since the earth is much more massive the force of the apple on the earth is negligible while the force of the earth on the apple is considerable thus the earth moves the apple further, but not faster, than the apple moves the earth.

The same for the 15 lb sledge hammer. The sledge is exerting a more powerful force on the earth than the apple did due to its greater mass but is still negligible considering the difference in mass between it and the earth thus the earth is also moving the heavier sledge further, but not faster, than the sledge moves the earth.

If all you had in the universe were the apple and the sledge hammer then the two would each exert a force on the other with the sledge having the greater force thus moving the apple further, but not faster, than the apple moves the sledge.


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ProtoTypical
Member
Posts: 1702
From: Ontario Canada
Joined: 08-04-2010


Message 7 of 81 (688103)
01-19-2013 2:03 AM
Reply to: Message 5 by Dr Adequate
01-19-2013 12:33 AM


Re: Equivalence Principal

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NoNukes
Member
Posts: 9529
From: Central NC USA
Joined: 08-13-2010
Member Rating: 3.2


Message 8 of 81 (688106)
01-19-2013 2:31 AM
Reply to: Message 6 by AZPaul3
01-19-2013 1:11 AM


Re: Equivalence Principal
If all you had in the universe were the apple and the sledge hammer then the two would each exert a force on the other with the sledge having the greater force thus moving the apple further, but not faster, than the apple moves the sledge.

Maybe I am misreading this, but your comment seems off. The gravitational force exerted on the earth by the moon is exactly equal and opposite to the gravitational force exerted on the moon by the earth. The resultant accelerations on the two bodies are different. The result is that the two objects orbit the moon-earth barycenter which is located inside the earth. The moon moves both farther and faster than the earth due to their mutual gravitational attraction.

Two objects of different masses falling towards earth experience the same acceleration because despite experiencing different forces proportional to their respective masses, each object resists accelerating in response to force due to its inertia, with said inertia also being proportional to its mass.

So the heavier object receives a larger force, but since a =F/m, the larger force results in the same acceleration generated by the smaller force on the smaller object.

Edited by NoNukes, : No reason given.


Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)

The apathy of the people is enough to make every statue leap from its pedestal and hasten the resurrection of the dead. William Lloyd Garrison.

If there is no struggle, there is no progress. Those who profess to favor freedom, and deprecate agitation, are men who want crops without plowing up the ground, they want rain without thunder and lightning. Frederick Douglass


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NoNukes
Member
Posts: 9529
From: Central NC USA
Joined: 08-13-2010
Member Rating: 3.2


Message 9 of 81 (688107)
01-19-2013 2:38 AM
Reply to: Message 1 by shadow71
01-18-2013 7:08 PM


Gravity is a phenomenon that results from the curvature of space-time. It likely existed at every moment after the big bang when there was any energy and any time and space.

I'd say that it is natural, but then I don't know what it would mean to call it metaphysical.


Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)

The apathy of the people is enough to make every statue leap from its pedestal and hasten the resurrection of the dead. William Lloyd Garrison.

If there is no struggle, there is no progress. Those who profess to favor freedom, and deprecate agitation, are men who want crops without plowing up the ground, they want rain without thunder and lightning. Frederick Douglass


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 Message 1 by shadow71, posted 01-18-2013 7:08 PM shadow71 has responded

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NoNukes
Member
Posts: 9529
From: Central NC USA
Joined: 08-13-2010
Member Rating: 3.2


Message 10 of 81 (688109)
01-19-2013 3:01 AM
Reply to: Message 4 by ProtoTypical
01-18-2013 11:53 PM


Re: Equivalence Principal
If the attractive force of gravity is proportional to the mass of two bodies, why does an object of greater mass not fall quicker?

If you wanted a huge big rock to accelerate the same as a small one, would you use a smaller or larger force on the big rock? Remember F=ma.


Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)

The apathy of the people is enough to make every statue leap from its pedestal and hasten the resurrection of the dead. William Lloyd Garrison.

If there is no struggle, there is no progress. Those who profess to favor freedom, and deprecate agitation, are men who want crops without plowing up the ground, they want rain without thunder and lightning. Frederick Douglass


This message is a reply to:
 Message 4 by ProtoTypical, posted 01-18-2013 11:53 PM ProtoTypical has responded

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petrophysics1
Member
Posts: 343
From: Boulder, Wy
Joined: 04-05-2006


Message 11 of 81 (688111)
01-19-2013 3:59 AM
Reply to: Message 4 by ProtoTypical
01-18-2013 11:53 PM


Re: Equivalence Principal
The force between objects is given by
F=Gx m1m2/d^2 ,G is a constant I'll just say it's 1.
d=1
m2=10,000

Let's look at two cases, one where m1=1 and one where m1=0.1

Case 1, F=Gx m1m2/d^2=1x 1x10,000/1^2= 10,000

Case 2, F=Gx m1m2/d^2=1x 0.1x10,000/1^2= 1,000

So in case 1 the force of gravity=10,000 and in case 2 the force of gravity=1000.............BUT

Since F=ma the acceleration a=F/m

case 1, a=F/m=10,000/1=10,000

case 2, a=F/m=1000/0.1=10,000

WOW, look at that, even though case 1 is 10 times the mass of case 2, they both have the same acceleration.

I guess they will fall the same which answers your question.

If the attractive force of gravity is proportional to the mass of two bodies, why does an object of greater mass not fall quicker?

P.S. It appears to me many people don't understand F=ma, this means that if you apply a CONSTANT force to an object it will go faster and faster. When people push a heavy object, after they overcome the force of friction, they "think" they are applying a constant force and the object isn't going faster and faster. So F=ma doesn't seem right, but they actually slack up a bit and ARE NOT applying a constant force. It's why people think Newton was a genius.

Edited by petrophysics1, : No reason given.

Edited by petrophysics1, : add P.S.

Edited by petrophysics1, : spelling


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shadow71
Member (Idle past 342 days)
Posts: 706
From: Joliet, il, USA
Joined: 08-31-2010


Message 12 of 81 (688120)
01-19-2013 9:14 AM
Reply to: Message 9 by NoNukes
01-19-2013 2:38 AM


My question is, are there any theories as to How Gravity came into existence?

Sorry for the typo in OP.

NoNukes writes:


I'd say that it is natural, but then I don't know what it would mean to call it metaphysical.

My question goes to the beginning of gravity. I cannot find any accepted theories as to how gravity came into existence.
Most say it is a natural phenomenon but give no scientific support for that position.

Have been reading Gerald Schroeder and he leaves me with the impression gravity is metaphysical in origin.


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ProtoTypical
Member
Posts: 1702
From: Ontario Canada
Joined: 08-04-2010


Message 13 of 81 (688121)
01-19-2013 9:20 AM
Reply to: Message 10 by NoNukes
01-19-2013 3:01 AM


Re: Equivalence Principal
Remember F=ma.

Well yes now I do remember it. I also have some vague recollection of having graduated from high school. I have a mind like an etch-a-sketch. While this keeps things fresh and interesting I sometimes feel like I have covered this ground before.


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AZPaul3
Member
Posts: 3427
From: Phoenix
Joined: 11-06-2006
Member Rating: 7.4


Message 14 of 81 (688122)
01-19-2013 9:26 AM
Reply to: Message 8 by NoNukes
01-19-2013 2:31 AM


Re: Equivalence Principal
Maybe I am misreading this, but your comment seems off.

Then it probably is. But no matter. There was a Rocky & Bullwinkle where Dudley Do-Right jumps from the bath and runs down the street yelling "Y-rika" instead of U-rika. The voice over explained that it was OK since Dudely know what he ment. I claim the same privilege.


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NoNukes
Member
Posts: 9529
From: Central NC USA
Joined: 08-13-2010
Member Rating: 3.2


Message 15 of 81 (688167)
01-20-2013 12:23 AM
Reply to: Message 11 by petrophysics1
01-19-2013 3:59 AM


Re: Equivalence Principal
When people push a heavy object, after they overcome the force of friction,

If friction is present, then you do have to apply a constant force just to keep an object moving at constant velocity.


Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)

The apathy of the people is enough to make every statue leap from its pedestal and hasten the resurrection of the dead. William Lloyd Garrison.

If there is no struggle, there is no progress. Those who profess to favor freedom, and deprecate agitation, are men who want crops without plowing up the ground, they want rain without thunder and lightning. Frederick Douglass


This message is a reply to:
 Message 11 by petrophysics1, posted 01-19-2013 3:59 AM petrophysics1 has not yet responded

    
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