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## What is the source for the force of gravity?

I remember that the force of gravity decreases with the distance from the center of the earth and that the gravity at the center of the earth is ZERO. If this is the case, then what is the source for gravitational force.

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## Closing Statement from Joe Varghese

Hi All,
Thanks a lot for your replies. I never thought that I would pull in this much of comments for a question like this. I will come back with more school kid questions later. Let me check my book of doubts, which I've been maintaining from my school days.

• #### Jacob Lynn

• +2
Apr 3 2012: The source of gravity as I understand, it is the effect of matter upon the fabric of space. Consider the fabric of space as being a large mattress, and the earth being a large 15 pound bowling ball. If you place the bowling ball on the mattress, it makes an impression, this is gravity. if you place a smaller, lighter ball close to the bowling ball it gets pulled in, much like the earth pulls objects in. So the source for the force of gravity is the effect of all the mass of matter of a given area upon the fabric of space. This is also why smaller, denser objects, such as dwarf stars, have a greater effect on gravity. My question is on black holes. For example, if you placed a small, extremely heavy ball on the mattress, it could tear through the mattress. This to me is how I perceive black holes working, an extremely dense object tearing through the fabric of space. Where did the object and all subsequent objects go? I seem to remember seeing somewhere that this has been produced in labs on a subatomic scale, where they make small particles that slip out of existence shortly after being made, possibly through tiny black holes that close moments after creation. Could they be exits to the pocket universes Mr. Anderson discussed?
• #### Don Stewart

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Mar 22 2012: Gravity is the opposite of levity. Levity arises from good jokes. Gravity, therefore, is the cosmic product of bad jokes - and occasionally good jokes told badly.
• #### edward long100+

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Mar 25 2012: Does a bad joke told well result in anti-gravity? Since only 2% of jokes are good maybe Cold Dark Matter is the product of bad jokes badly told. Hmmm.
• #### Don Stewart

• +1
Mar 27 2012: Cold, dark matter is the result of the grave, not gravity. It's a subtle etymological distinction, obscured all the more by the cryptic culinary reference in Dickens' Christmas Carol, long thought to be a typo: "There's more of gravy (sic) than of grave about you...".
• #### edward long100+

• +1
Mar 28 2012: dripping gravy accelerates at 32 ft. per second per second until it impacts the fabric of the spiller's shirt where, over time, it becomes cold, dark matter. So the answer to Mr. Varghese's question is simply "Bad Jokes are the source of the force." See you in Stockholm later this year!
• #### edward long100+

• +2
Mar 22 2012: There are THEORETICAL force-carrying particles called gravitons. According to wave/particle duality and associated with gravitational waves (which are ripples of space/time curvature traveling at the speed of light) gravitons are yet to be observed. Gravity always acts as an attracting force on every mass in the Universe. If an opposite force acts equally on the same mass the illusion will be "zero gravity".
• #### Karl Sjostedt

• 0
Mar 29 2012: Except that chunks of matter cannot be the underlying nature of the universe. It has to be something smooth like vibrations or waves. Forces just seem to exist because we reduce the waves to particles.
• #### edward long100+

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Mar 29 2012: It's turtles all the way down!
• #### James Howells

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Mar 21 2012: ...its not so much gravity is Zero as much as gravitational pull in one particular direction is no more than any other, so we would feel zero effects of gravity, It's there just pulling equally in all directions and therefor not felt. So the source is still the earth.
• #### Pedro Maschio

• +1
Mar 25 2012: sorry, I did not mean to offend or be sarcastic, I really do not understand what you mean by scientific test in the context of your comment. I agree we should not say God to all questions. I meant that gravity is one question we do not have an answer to, like we do not have an answer to "does God exist". God is the answer when we have no other answer.
• #### Brooke Clarke

• +1
Mar 24 2012: Richard Feynman addressed this question in the Messenger series of lectures on Microsoft Tuva.
http://research.microsoft.com/apps/tools/tuva/index.html#data=3%7C%7C%7C
The short answer is no one knows how gravity works, unlike other parts of physics.

Have Fun,

Brooke
• #### Francis Coderre

• 0
Apr 19 2012: The force of gravity has basically the same formula than the electromagnetic force. The gravitational force between two objects is the product of their masses divided by the distance squared (times a constant) and the electromagnetic force between two charges is their product divided by the squared distance (times a constant). Gravity is only an attraction force, but charges attract each other only if they are of opposite sign. It seems that all cosmic bodies attract each other, I have never heard of repulsion between stars or other celestial bodies. Anyway, I have another question, what is the source for electromagnetic force. I guess the easy answer would be that the source of gravity is matter as the source of electromagnetism is charge.

Also what do you mean by the source ? As if all force have sources ? When we say the source of energy for example powering a car or a computer or you, the source is just another force transformed into this one. Matter has no source, it was always there. As for matter, the total amount of force is fixed (equal to infinite). It can only transform.

And asking WHY is matter attracting other matter is a false question, the matter does not care, it does not need a reason to do so. But you dindn't so we're good. I do not know how gravity works, but my guts tells me it's electromagnetic even though it's probably the only force that scientists agree it's not.

Inertia is the tendency of an object to keep it's SPEED and direction, it is KINETIC in nature. Inertia completes gravity in the dynamic governing the orbit of a planet around another body. When you draw it on a peice of paper, there is two arrows, a force pulling towards the sun and a force pulling in the way it's already going (so to speak). The sum of the two keeps the planet in orbit. Wether energy is potential gravitational or kinetic, or electromagnetic, it's amount is fixed, and the three states coexist in a balanced way. Force is always linked to matter somehow, cant help
• #### Simply Noor

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Apr 8 2012: Thanks for replying Frodo.
• #### Tuvia Basser

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Mar 29 2012: Gravity originates in anything and everything with mass.
When we talk about the gravitational force of the Earth, we mean the net effect of all parts of the earth acting together.
The net effect of all parts acting together is zero at the center of the Earth, because the gravity of the parts to the north is equally balanced by gravity of the parts to the south, etc.
• #### Simply Noor

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Mar 28 2012: Is it possible that actually gravity is not some force that is pulling inside towards the Earth but some force from outside that is forcing down to Earth?
• #### Frodo Baggins

• +1
Apr 3 2012: What is down? There is no "down". North South East West don't exist as absolutes in the universe. They are convenient abstract concepts invented by humans.

Gravity does not point "down". Its points to the center of mass. There cannot be a force from outside pushing you down because in that case the earth wouldn't orbit the sun and you wouldn't exist.

Because the sun pulls the earth, and the earth is moving away from the sun at just the right speed, you have orbit. You can try this yourself. Take a piece of string, and tie a rock around it and swing it around...the string represents gravity, it is pulling the rock into a circular orbit, if the string snaps, the rock flies off. That is how orbits work.

Gravity is the invisible string. It pulls things towards each other. The sun is much more massive than the earth, so it is the earth that is pulled towards the sun with a greater force.

You cannot explain orbits with gravity being an external force that pushes everything "down"
• #### Simply Noor

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Apr 4 2012: Hi Frodo

if you dont mind can you please answer me...
is that the mass of sun affecting the solar system...the planets ? or the masses of the planets also affect each other? if yes....then what would happen if all of them come in a linear position along with Sun?
• #### Frodo Baggins

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Apr 4 2012: all mass has gravity. in our solar system the sun is the most massive object. the sun is 1000 times more massive than the most massive planet, jupiter. all of the planets combined do not affect the sun, its like a bunch of ants trying to pull an elephant. It seems highly unlikely that all the planets will line up at along the same axis, because the orbital planes of the planets are not parallel to the center of the sun. The inclination of earth's orbit is 7 degrees.So in the physical universe, in our solar system all planets can never line up precisely the way you want them to. And even if such an event occured....whats the issue?... nothing magical happens when two planetary bodies line up with the sun....gravity doesn't stop working. Gravity doesn't stop working when you have a solar or lunar eclipse.The solar system is approximately 4.5 billion years old. Nothing catastropic has happened in this period of time. It is an unthinkable amount of time.

Relevant: http://www.nasa.gov/topics/earth/features/2012-alignment.html

Also further, if you posit that something spectacular will happen once all the planets line up, show me the calculations. Thanks
• #### Subhra Dhar

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Mar 26 2012: Yes, I think you are right.
• #### Kathleen Herzog

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Mar 26 2012: Suppose the Earth did not turn, as the center is essentially 'still', there is no energy applied foward or back [acceleration/zero velocity], so Gravity is essentially the effect of opposing forces. The question may be re-phrased: How does centrifugal force affect objects at the outer edge of the radius as opposed to the inner core? Or: Does gravity have a source? Or: Is gravity the result of opposing forces?
Newton created mathematical equations for these questions, have they been disproved? ARGH< another question.......
• #### Frodo Baggins

• +1
Apr 3 2012: You are mixing a lot of terminology. Centrifugal force is a fictitious force. It is the force you feel when you take a hard turn in your car, where your body is pushed in the opposite direction than of the turn.

Mass is the source of gravity. Gravity is an attractive force, unlike magnetism. There are no opposing gravitational fields. Newton did not create mathematical equations for anything that you are describing...

In regards to the center of the earth...imagine a ball of yarn. How does it start? It starts off as a small ball, and you keep spinning yarn on top, until you have a really big ball. Are there any opposing forces inside the ball of yarn.. ? No. The center of the ball of yarn is under compressive force, and all forces are directed inward, towards the center.

Ant any given point on this ball of yarn, the force will be inward, because if that were not the case, the ball would fall apart. The center of the earth is immensely massive (not in terms of size or volume) but in terms of mass (density). It is compressed together into a really small space...and everything else is pulled towards the center.

Gravity explains why heavenly bodies are roughly spherical. A sphere is the only geometric shape that is symmetric about any central axis.

If you have a soup of particles that have the property of gravity the particles will coalesce around the center of mass/gravity of the system. A sphere is infinitely symmetrical and also the shape with the lowest Surface Area per unit volume. So it is the most efficient, compact shape possible, and this is because all the particles share a common "center of gravity", and the forces on any given particle from a fixed distance from the center are uniform.

The sun is not a cube, because the forces on the surface of a cube would be asymmetric, the pointy ends would be under less force than the sides of the cube and inevitably the mass would fall inwards until it was spherical.
• #### Kathleen Herzog

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Apr 3 2012: Ahh, thank you, way out of practice. Now about the Black Hole, is it caused by a super dense object traveling at a speed that allowed it to rip through the space 'mattress', pulling everything behind it?
• #### Frodo Baggins

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Apr 4 2012: I do not know much about black holes. But you are right about it being a superdense mass.

Blackholes are caused by stellar matter collapsing in, on itself, in some rare circumstances. It warps space because of its mass, it doesn't puncture through the fabric of space.

I personally have a very hard time imaging "empty" space i.e. vacuum being warped and being influenced by gravity
• #### Krisztián Pintér200+

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Mar 25 2012: in the middle gravity is zero because pulling from different directions cancel each other out. like taking a step to the left, the to the right. in effect, you didn't move.
• #### Subhra Dhar

• 0
Mar 25 2012: Gravity, is a natural phenomenon by which heavenly bodies (stars, planets, satellites etc) attract with a force proportional to their mass. Gravitation is responsible for keeping the Earth and the other planets in their orbits around the Sun; for keeping the Moon in its orbit around the Earth.
• #### James Howells

• +1
Mar 25 2012: Isn't there gravitational pull between all objects...just relative to their mass?... I always thought it didnt have to be a " heavenly" body. Like you have a gravitational pull with your computer right now it is just so much less than that of the earths pulling it onto your desk or couch or bed...
• #### Karl Sjostedt

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Mar 29 2012: yep mass and gravity go hand in hand if something has mass then it has a gravitational pull. If it seems that a phenomena is re-enforced in the direction of another phenomena we say that the phenomena has mass and say that there is a force pulling the phenomena towards eachother. Both mass and gravity are just ways of talking about phenomena we observe. There are no chunks with mass being pulled by forces it is really just vibrations re-enforcing eachother making it seem as if chunks are being pulled towards other chunks. It is easy and useful to talk about mass and gravity in reference to most problems we want to solve rather than looking at the maths of centers of vibration and harmonic re-inforcement.
• #### Vicky Smith

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Mar 21 2012: simple answer to a simply question = god. god created everything and force was one of those.
• #### Gerald O'brian50+

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Mar 22 2012: Brilliant.
• #### James Howells

• +3
Mar 22 2012: Ok...that may be true but don't put that answer on a science test. Not because its "wrong" But you could go through every single question on Ted and say God. Personally I think God enjoys us asking questions and exploring his world and trying to find the answers to the tough questions.
• #### Pedro Maschio

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Mar 25 2012: James, replace "God" with "Elementary rules of the universe". Gravity is what keeps the balance of the universe, prevents planets and stars from shocking to each other, and keep galaxies "running". It is the base, the start, the energy, the everything. We are limited by space, time, light and gravity - that defines the boundaries of our universe. We cannot explain gravity as much as we cannot explain how the other 3 started in the universe. Maybe the explanation of God is: the space, time, light and gravity in which we live. A science test... what does that mean?
• #### James Howells

• 0
Mar 25 2012: Ok... where would we be if we SIMPLY answered God to every question ever presented to us?

As for what is a science test...I cant read if your being sarcastic...put one of these if you are...(:P), I will assume you were.