Gravity: How does it work?

[PistolPete38]

I got thinking the other day about gravity (dont ask me why, sometimes my mind goes off on tangents). I thought about high school science about how gravity works and realized i never got an explanation that satisfied me. I remember being told gravity is created by the mass of whatever body generates it, the greater the mass the greater the gravity. What i dont understand is how? Is it due to elecro-magnetic fields that they generate, the larger the mass the stronger the magnetic field? Any information you can provide would be appreciated.

[mezarashi]

Why you are probably thinking of the same problems physicists after Newton thought about. Newton created the concept of gravity and his principles of mechanics made use of gravity. He says it exists but he never explained why and or the mechanism on which it works.

 

If you think about your question carefully, it can be extended. Why does mass exert and is subjected to gravity? Why does charge exist? Why are there exactly TWO types of charges, positive and negative? Why do they attract and repel? Why are there gravitational fields? Why are there electromagnetic fields?

 

The simple answer is that these are the fundamental properties of our physical universe. These are the rules of the game. It exists, we know it exists and we know how they work. Why they are there as such is very philosophical.

 

There is alot of theoretical research into theories that will actually explain/be able to derive these forces. Einstein's general relativity is such a case with gravity resulting from the warping of the space-time continuum due to matter.

[swansont]

Gravity is not electrical nr magnetic in nature. Classically, it is due to mass but AFAIK Newton proposed no real mechanism. According to GR, mass and energy curve space, which affects the trajectory of things passing through it.

[BigMoosie]

A popular idea these days is that a massless particle called a graviton is given off by mass and when that hits matter it instructs it to accellarate towards it.

[PistolPete38]

Interesting, not really what i was hoping for but it helps.

 

bigmoosie the graviton theory is interesting but how can a particle be massless, isnt that an oxymoron. Perhaps i am just dense tonight but i dont quite follow your explanation on how gravitons supposedly work.

 

The way i see it it is like the chicken and the egg, you cant identify the mechanism of gravity without knowing how the mechanism works and vice versa.

 

Another thing that confuses me is how gravity and centrifical force work similarly but opposite. Gravity will hold you to the surface of a spinning object such as the surface of earth while centrifical force you have to be inside the spinning object to maintain footing for example how some space stations will theoreticaly produce artificail gravity by having a section that spins. Both mechanisms produce the same general effect but oppositely. Does this make sense to anyone or am i way off here.

[BigMoosie]

Recall that the photon is also massless.

Gravity causes me to accellarate towards the ground, a centrifuge (note that there is not such thing as centrifugal force) is when a surface accellarates into me, either way the two bodies are accellarating towards each other so they really are exactly the same.

[Mobius]

Gravity is still causing problems in physics today.

 

It is completely different from the three other natural forces (electromagnetic, strong and weak nuclear forces) due to weakness. Gravitational forces for small masses is negligible capared to the other forces.

It is thought that at an extremely high temperature that all forces were the same i.e. close after the big bang. Although the strength of the force is weak its range is infinte compared to the short range of the others.

 

The graviton theory is based on an "exchange particle". Forces work by exchanging particles (electromagnetic forces exchange photons etc...). This "exchange particle" means that objects feel the force by exchanging gravitons.

 

Gravitons and their wave equivalent (gravitaitional waves) have not yet been discovered or confirmed (as far as I know).

 

The problem with Newton's picture of gravity was that it did not include time. So according to Newton Gravity was instantaneous. If the sun disappeared right now we would feel the effects right now and career on a tangent out of the solar system. This is not the case we would not feel the effects for another 8 mins. Einstein showed that gravitational effects travel at the speed of light.

 

As already mentioned General relativity sees gravity as curved space and objects travel the path of least resitance within that curved space. And indeed if gravity gets very strong it can curve space into a singularity i.e. a black hole.

 

As I said gravity is still causing problems as it cannot be combined with quantum mechanics. The problem is not only the extreme difference in the nature of the magnitude of the force but also the "smoothness" of gravity. Gravity casues a curve in space that should be smooth. Quantum space is very different as it is a see of virtual particles and destroys this smoothness.

 

Most modern theories are trying to rectify the situation. M theory (a combination of 5 different string theories) is one of the best models to combine gravity with the other forces and to fully understand what this mysterious force that keeps us to this earth.

 

Or you could say it's just magic!!!!

[mezarashi]

Interesting' date=' not really what i was hoping for but it helps.

 

bigmoosie the graviton theory is interesting but how can a particle be massless, isnt that an oxymoron. Perhaps i am just dense tonight but i dont quite follow your explanation on how gravitons supposedly work.

 

The way i see it it is like the chicken and the egg, you cant identify the mechanism of gravity without knowing how the mechanism works and vice versa.

[/quote']

 

Are you more interested with the reason gravity exists or rather the mechanism in which it works? How gravity works is understood relatively with today's physics. You can see them mentioned in the other posts in this thread so far.

 

Another thing that confuses me is how gravity and centrifical force work similarly but opposite. Gravity will hold you to the surface of a spinning object such as the surface of earth while centrifical force you have to be inside the spinning object to maintain footing for example how some space stations will theoreticaly produce artificail gravity by having a section that spins. Both mechanisms produce the same general effect but oppositely. Does this make sense to anyone or am i way off here.

 

This confusion is from the techniques used to model and solve problems involving gravity on objects in circular motion. It doesn't have to do with how gravity works or the causes of gravity. You have to understand that there is no such thing as the centrifugal force. It is a virtual force created purely to aid us in modeling the system. I've seen multiple threads discussing "centripetal versus centrifugal forces" in the context of gravity in more detail.

[Mobius]

The "artificial gravity" from a spinning object is when the centripetal force balances the gravitational force. Einstein stated that the two forces were equivalent. Satellites stay in orbit by balancing their centripetal force with the gravitational force from the earth.

[swansont]

The "artificial gravity" from a spinning object is when the centripetal force balances the gravitational force. Einstein stated that the two forces were equivalent. Satellites stay in orbit by balancing their centripetal force with the gravitational force from the earth.

 

Sorry, but that's worded somewhat awkwardly. It seems like you are using "balance" to mean "equal to" but it might not be read that way to the uninitiated. Artificial gravity is present because of the centripetal force, exerted by the space station walls, in the absence of gravity. And when satellites travel in their orbit, the centripetal force is the gravitational force; there are not two forces present that cancel.

[Mobius]

Ok I'm with you on the gravitational effect on the walls of a rotating space station, that is not in a gravitational field, is due to centripetal force.

 

However I am unsure of what you mean by the fact that the two forces are not balancing the gravitational force of the earth. All satellites of the earth experience the earths gravitational field.

 

Do you mean that they are effectively in free fall and do not feel the gravitational force? So it falls around the earth's surface as opposed to on it.

 

I honestly thought that there was a "balancing" effect. As is the case: the nearer the satellite is to the earth, the faster it must go. Even high school students must equate the formulas for centripetal force with gravitational force in order to work out their height.

 

Just explain the fact that the two forces don't cancel. Is it because it is the fact that you are moving in a circle in a freefall fashion and therefore the only force experienced must be centripetal, keeping us in that circle. However you must account for the fact that if we did not have this centripetal force we would plunnit towards the ground due the the earths gravity!

[ydoaPs]

don't believe them! they are hethans out to make the world fornicate. trust this.

[Klaynos]

A satalitte is moving in orbit around the earth there is only ONE force acting on it, gravitational force. Nothing else. This gravitational force is towards the centre of a circle, as the satalite also has some velocity parellel to the earths surface at ever point. As it is a force towards the centre of a circular motion then it is a centralpetal force and can be equated as both a centralpetal force and a gravitational force, but they are the SAME force.

 

There is nothing trying to pull the satalite away from the earth, if gravity stops then it does not fly outwards, it goes in a streight line due to it's current velocity, which as there is no force to change this velocity it goes streight along a tangent from it's previouse orbit.

[Mobius]

Ah yes Is see they ARE the same force now, it has been some time since I thought about satellites and circular motion in that way. It is far easier to mess around with the equations without thinking what is really going on. I think that goes for most of physics

[Klaynos]

Ah yes Is see they ARE the same force now, it has been some time since I thought about satellites and circular motion in that way. It is far easier to mess around with the equations without thinking what is really going on. I think that goes for most of physics

 

Which is why the secret to teaching it is not teaching people a few forumlae and testing their usage but teaching them to understand and testing their understanding...