Is gravity really a force?

[spikerz66]

everything

[dstebbins]

everything

 

elaboration would be nice.

[spikerz66]

its hott

[Cap'n Refsmmat]

Back on topic please.

[dstebbins]

Back on topic please.

 

yes, let's please get back on topic.

[JohnF]

What's the difference between the effect you feel at an acceleration of 1G and the force you feel on the ground?

 

Maybe all objects are accelerating through an unknown dimension and what we feel is the effect of that acceleration. Objects attract each other because of a disturbance they create in this dimension.

[Klaynos]

What's the difference between the effect you feel at an acceleration of 1G and the force you feel on the ground?

 

When you're on the ground there is an equal and opposite force pushing upwards on you. And the force due to gravity isn't g, it's g x mass. An acceleration of 1g is just an acceleration of 9.81m/s/s

[JohnF]

When you're on the ground there is an equal and opposite force pushing upwards on you. And the force due to gravity isn't g, it's g x mass. An acceleration of 1g is just an acceleration of 9.81m/s/s

 

But the mass of an object determines how it accelerates through this other dimension. So the planet is pushing 'upwards' on us. We are carried through this dimension with the planet. We still have our own gravity because we are also accelerating at a much smaller rate through this dimension.

[Klaynos]

Could you back this idea with some maths?

[Aurorum]

I am enjoying this. ;-)

[Royston]

But the mass of an object determines how it accelerates through this other dimension. So the planet is pushing 'upwards' on us. We are carried through this dimension with the planet. We still have our own gravity because we are also accelerating at a much smaller rate through this dimension.

 

I don't understand why an extra dimension is needed, you can describe this behaviour with something as simple as a vector...net force = 0.

[JohnF]

Could you back this idea with some maths?

 

No. But then what comes first, the idea or the proof? It's just an idea and how you view it is your choice. You could decide that the idea has no validity at all and ignore it. You could choose to think about it for a while and see if a mathamatical explanation can be created. Even if the math can be developed, it may not prove the idea anyway.

 

But what you can't do is prove it is invalid just by asking "Could you back this idea up with some maths?"

 

Why not discuss the implications/pitfalls of it?

 

Anyway, it does seem to have got the thread back on topic

[JohnF]

I don't understand why an extra dimension is needed, you can describe this behaviour with something as simple as a vector...net force = 0.

 

I have no idea either. I just assumed that if the planet is accelerating to cause the effect of gravity then it couldn't be accelerating through normal space; the Australians would all fall off. So it must be accelerating through some other dimension.

[Klaynos]

No. But then what comes first, the idea or the proof? It's just an idea and how you view it is your choice. You could decide that the idea has no validity at all and ignore it. You could choose to think about it for a while and see if a mathamatical explanation can be created. Even if the math can be developed, it may not prove the idea anyway.

 

But what you can't do is prove it is invalid just by asking "Could you back this idea up with some maths?"

 

Why not discuss the implications/pitfalls of it?

 

Anyway, it does seem to have got the thread back on topic

 

I'm going to say some experimental result or the maths comes first...

 

This idea of acceleration of massive particles causing them to have mass rings a bell for some reason though. Have you googled it extensively?

[JohnF]

This idea of acceleration of massive particles causing them to have mass rings a bell for some reason though. Have you googled it extensively?

 

Sorry, not at all. It was just an idea I had after looking at this thread. It's not unusual for me to say what I'm thinking without first thinking about it

 

I did invent a neat device on another forum that way though; so sometimes it pays off.

 

I have just read in another thread on here something about inertia and gravity.

[bombus]

Refrain from Spouting off this Pseudoscience and claiming it as Fact!

 

I thought gravity was an effect (of matter warping spacetime), rather than a force like, say, electricity...

 

I also though the effects of accelaration are indistinguishable from gravity. This is why a rotating object is in constant accelaration even if its velocity is constant - hence artificial gravity on rotating space stations.

 

Am I right???

[timo]

I thought gravity was an effect (of matter warping spacetime), rather than a force like, say, electricity.... I also though the effects of acceleration are indistinguishable from gravity.

Forces only exist as something real if you restrict the allowed coordinate systems to certain classes. If you have a movement following the equation of motion [math] x(t) = ct^2 [/math] with c being any constant (or constant vector of R³ if you prefer), then you have the acceleration [math] a = \ddot x = \frac{d^2x}{dt^2} = 2c [/math] and by [math]F=ma[/math] can state that a force of [math] F=2mc [/math] was working. If you describe the motion of the same object with coordinates [math]x'[/math] which transform from old coordinate system by [math]x' = x - ct^2[/math], then obviously [math] x'(t) = 0 \Rightarrow a' = 0 \Rightarrow F'=0 [/math], where [math] a' [/math] and [math] F' [/math] mean acceleration and force in the new system, respectively.

So the question whether a force is working on the object or not becomes a matter of perspective. A common example fitting to that calculation is someone in free-fall in an elevator. For a person inside the elevator, there is no measurable force since he/she is floating weightless inside the cabin. For someone standing outside on the surface of earth, the whole system seems to be accelerating due to gravity, with a potentially unpleasant outcome for the person inside the elevator.

The argument about forces being dependent on perspective is not restricted to gravitational attraction, though. Above calculation only assumed a constant force in some coordinate system which was canceled by chosing an appropriate other coordinate system. Whether the force was a gravitational or an electric one doesn´t matter for this example.

 

For different geometries, different coordinate systems are practical. In GR, gravity is described by giving spacetime some dynamic properties (which play an analogous role as the "field" I mentioned here). Adding a mass to spacetime alters these properties, which can lead to your old coordinate system not anymore having the nice properties for which you have chosen it previously. As a result you can now have a force acting where no force was acting before. So in some sense the warping of spacetime induces a force. But you can in principle again do a coordinate transformation to a new coordinate system where the force vanishes.

 

Sidenote: Note that the term "force" is sometimes used synonymiously for "interaction" and not in its closer sense.

[Royston]

I have no idea either. I just assumed that if the planet is accelerating to cause the effect of gravity then it couldn't be accelerating through normal space; the Australians would all fall off. So it must be accelerating through some other dimension.

 

I realize you've buried the idea now, but a few pointers, just incase you're not aware.

 

I'm not sure if you're joking about Australians falling off, but remember there's no such thing as preferred frame of reference, so there's no 'top' of the earth, we have north, south et.c for convenience, and it works from the earths frame of reference, but as soon as you leave the earth, north and south become obsolete. The universe is homogenous i.e one co-ordinate cannot be considered more important than another, so space is very dynamic in that sense.

 

So gravity is space curving towards earth from all directions, hence nothing is falling off. Where there's mass, there's curvature...imagine the pinch effect in photoshop, but in 3 dimensions.

 

The only thing I can think off with regards to accelerating bodies and increasing gravity is Unruhs Law. This law hasn't been tested experimentally AFAIK, but it states that an accelerating body increases in heat, that means an increase in energy...more photons, more mass, so a stronger gravitational field. So I presume this has to be tested in a vacuum, as obviously there has to be no friction for the law to hold.

 

Sorry if you know most of this, I'm not sure what background you have in physics.

 

EDIT: If I got the last bit wrong, could somebody correct me on Unruhs law.

[swansont]

I realize you've buried the idea now, but a few pointers, just incase you're not aware.

 

I'm not sure if you're joking about Australians falling off, but remember there's no such thing as preferred frame of reference, so there's no 'top' of the earth, we have north, south et.c for convenience, and it works from the earths frame of reference, but as soon as you leave the earth, north and south become obsolete. The universe is homogenous i.e one co-ordinate cannot be considered more important than another, so space is very dynamic in that sense.

 

There's no preferred inertial frame, but an accelerating frame can be distinguished from an inertial one. I think the idea is that if gravity were actually just an acceleration, you'd have to have it be toward the center of the earth; if it were in the direction of the earth's motion then not everyone would feel it in that direction. It's not in x, y or z, so you postulate a new dimension, q, that is orthogonal to all of them. So gravity is equivalent to acceleration in q. But that means that two people in differing gravity are moving apart in q-space. What does that mean?

 

I think you have to look at things in polar coordinates, too. The acceleration is in the -r direction, which is not a new dimension.

[JohnF]

There's no preferred inertial frame, but an accelerating frame can be distinguished from an inertial one. I think the idea is that if gravity were actually just an acceleration, you'd have to have it be toward the center of the earth; if it were in the direction of the earth's motion then not everyone would feel it in that direction. It's not in x, y or z, so you postulate a new dimension, q, that is orthogonal to all of them. So gravity is equivalent to acceleration in q. But that means that two people in differing gravity are moving apart in q-space. What does that mean?

 

I think you have to look at things in polar coordinates, too. The acceleration is in the -r direction, which is not a new dimension.

 

You've hit the nail on the head for me there swansont, thanks. This is what I mean by another dimension. It would also mean that each atom accelerated through this dimension as a separate entity, but as a whole the total acceleration of all the atoms gives us the total gravity of the planet. I realize that within the other dimension things would be moving apart but does that necessarily mean they should move apart in space.

 

You could also look at this as a negative acceleration but that would mean everything would have to stop eventually; so perhaps not.

 

But if the acceleration did exist in this other dimension then, if I had the skills, I would start looking for a relationship between that, the expanding Universe and the effects of time dilation.

 

Yes I was joking about the Australians falling off, everyone knows Australia is magnetic and they wear iron soled boots

[Royston]

There's no preferred inertial frame, but an accelerating frame can be distinguished from an inertial one. I think the idea is that if gravity were actually just an acceleration, you'd have to have it be toward the center of the earth; if it were in the direction of the earth's motion then not everyone would feel it in that direction. It's not in x, y or z, so you postulate a new dimension, q, that is orthogonal to all of them. So gravity is equivalent to acceleration in q. But that means that two people in differing gravity are moving apart in q-space. What does that mean?

 

I think you have to look at things in polar coordinates, too. The acceleration is in the -r direction, which is not a new dimension.

 

Right, I see where JohnF is coming from now...JohnF, sorry, when in doubt listen to the expert not the newbie

 

Thanks for the correction Swansont.

[JohnF]

Right, I see where JohnF is coming from now...JohnF, sorry, when in doubt listen to the expert not the newbie

 

That's OK Snail; that makes me a newbie, newbie. The problem I have is trying to describe something that I can barely visualise.

 

But I just can't believe you didn't realise I was joking about the Australians

[Royston]

But I just can't believe you didn't realise I was joking about the Australians

 

Neither can I, sorry about that...sometimes, especially with new members, it's hard to gauge what they know, when they're joking et.c You do get some questions on here that defy belief, that really require just a little thought for the answer, obviously there's nothing wrong with asking questions, and everyone here is happy to help, but it does happen on occasion, so it's easy to get crossed wires.

 

It's interesting though, that a question such as 'why don't Australians fall off the Earth' actually requires a lot of explanation. Just saying 'it's gravity' is obviously not suffice, and to answer the question properly does involve explaining some rather counter intuitive concepts.

 

Apologies for veering of topic.

[swansont]

It's interesting though, that a question such as 'why don't Australians fall off the Earth' actually requires a lot of explanation. Just saying 'it's gravity' is obviously not suffice, and to answer the question properly does involve explaining some rather counter intuitive concepts.

 

Apologies for veering of topic.

 

 

"Gravity is a radial vector" is the short answer, since it includes the notion of there not being an up and a down. People falling off has (perhaps subtle) ties to the concept of the earth being flat.

 

But, to again veer off topic, my boss and I were giving a tour of our lab to an Admiral, and discussing our vacuum system. The admiral made the joke about a vacuum keeping hot things hot and cold things cold — how does it know? My boss (who has a good sense of humor) was so locked in to the "explain technical thing to impress the admiral" mode that he started explaining the thermal insulation properties of a vacuum, until I pointed out that it was a joke. So you're not alone in focusing so much that you are missing what is often obvious. (I've done it, too)

[Norman Albers]

This is a spherically symmetric system, or nearly. You can go around the Earth and not fall off, at least off the Earth.