Gravitational field of earth

Could someone please explain this to me?

Q: "If the Earth was indeed a flat disc, wouldn't the whole planet crunch up into itself and eventually transform into a ball?"

A1: If the Earth generated a gravitational field, yes, it would eventually happen, after a billion years maybe. FE assumes that the Earth does not generate a gravitational field.  What we know as 'gravity' is provided by the acceleration of the earth.

This is from the FAQ. This makes no sense. All matter (anything having mass) generates a gravitational field, even you and me. This was proved by the Cavendish experiment. I also performed this experiment in a college class.

How does the earth magically not generate a gravitational field?

This is a good question. I personally feel a FE model with a rotating earth exhibiting gravitation is more likely, but I'd be interested to hear the opinions of those FEers who think the Earth does not have a gravitational field.

Cavendish is not an experiment showcasing gravity, only torsion of a rod or wire.

Robbyj, the Cavendish experiment IS meant to showcase gravity. The Cavendish experiment, done in 1797 – 1798 by Henry Cavendish, was the first experiment to measure the force of gravity between masses in the laboratory.

It did nothing of the sort.

What the hell are you talking about? The point of the experiment was to show everything produces a force on other objects due to its gravitational field! Hell, he was able to determine the gravitational constant for god sakes.

Robbyj, the Cavendish experiment IS meant to showcase gravity. The Cavendish experiment, done in 1797 – 1798 by Henry Cavendish, was the first experiment to measure the force of gravity between masses in the laboratory.

No, it only tried to measure the density of the Earth and perhaps predicted G.

Cavendish is not an expirement showcasing gravity, only torsion of a rod or wire.

It is not true that the experiment showcases torsion, although minimizing torsion is a very important part of the apparatus. Building a device that has near-zero torsion is critical because the force of gravity movement along geodesics due to small masses is incredibly small. You can do the experiment yourself.

When you compare multi-mass systems you are literally bending spacetime, as defined by Einstein. (In the Cavendish experiment, you are moving the position of masses, thus manually bending spacetime.) Einstein also said that for non-extreme cases this is proportional to the masses involved.

Sure, gravity doesn't exist. But large masses such as the Earth (flat or round) bend spacetime significantly, causing a lot of motion along geodesics.

For some reason, many FE folks who hold Einstein up as the messiah of spacetime, in their zeal to deny gravity, insist that the Earth's mass have no effect on spacetime whatsoever. 

Quote from: clydedaferret on August 23, 2008, 09:16:40 PM

Robbyj, the Cavendish experiment IS meant to showcase gravity. The Cavendish experiment, done in 1797 – 1798 by Henry Cavendish, was the first experiment to measure the force of gravity between masses in the laboratory.

No, it only predicted G.

Yes! Which used the fact that all objects exert forces on others by their gravitational fields!

Gravitational constant != force of gravity. The experiment did not prove gravity.

Quote from: Jack. on August 23, 2008, 09:26:31 PM

Quote from: clydedaferret on August 23, 2008, 09:16:40 PM

Robbyj, the Cavendish experiment IS meant to showcase gravity. The Cavendish experiment, done in 1797 – 1798 by Henry Cavendish, was the first experiment to measure the force of gravity between masses in the laboratory.

No, it only predicted G.

Yes! Which used the fact that all objects exert forces on others by their gravitational fields!

Not in the least.

Without the force of gravity, the experiment wouldn't make any sense.

It seems that we are in agreeance.

No, we aren't. I conducted the experiment myself. There is clearly an attractive force between objects.

Also:
The gravitational constant, denoted G, is a physical constant involved in the calculation of the gravitational attraction between objects with mass.

Also:
The gravitational constant, denoted G, is a physical constant involved in the calculation of the gravitational attraction between objects with mass.

Right, so how does that equal to gravity itself?

I never said it did. All I am saying is that the experiment helped produce that constant which is used to calculate the force due to gravitational forces between two (or more) objects.

All I am saying is that the experiment helped produce that constant which is used to calculate the force due to gravitational forces between two (or more) objects.

So you admit that you were wrong about the experiment earlier?

which is used to calculate the force due to gravitational forces between two (or more) objects.

Oh really?

What? How would that be admitting I am wrong. I am not wrong.

According to the law of universal gravitation, the attractive force (F) between two bodies is proportional to the product of their masses (m1 and m2), and inversely proportional to the square of the distance (r) between them:

    F = G \frac{m_1 m_2}{r^2}.

What? How would that be admitting I am wrong. I am not wrong.

This,

the Cavendish experiment IS meant to showcase gravity.

According to the law of universal gravitation, the attractive force (F) between two bodies is proportional to the product of their masses (m1 and m2), and inversely proportional to the square of the distance (r) between them:

    F = G \frac{m_1 m_2}{r^2}.

Ok, now use your equation to calculate the force between the sun and a photon.

Quote from: clydedaferret on August 23, 2008, 09:44:11 PM

According to the law of universal gravitation, the attractive force (F) between two bodies is proportional to the product of their masses (m1 and m2), and inversely proportional to the square of the distance (r) between them:

    F = G \frac{m_1 m_2}{r^2}.

replace m_2 with the equation (hf)/c^2 where h is plancks constant f is the frequency of the photon and c is of course the speen of light and then you can go ahead an calculate the force between the 2 objects

Ok, now use your equation to calculate the force between the sun and a photon.]

Quote from: clydedaferret on August 23, 2008, 09:42:29 PM

What? How would that be admitting I am wrong. I am not wrong.

This,

Quote from: clydedaferret on August 23, 2008, 09:16:40 PM

the Cavendish experiment IS meant to showcase gravity.

You use the words gravity and gravitation in your FAQ and don't do so exact distinction between then. If you are so precise about their use then put the definition of "gravity" and "gravitation" on your FAQ

There is a sticky that defines "gravity" and "gravitation".

Quote from: clydedaferret on August 23, 2008, 09:44:11 PM

According to the law of universal gravitation, the attractive force (F) between two bodies is proportional to the product of their masses (m1 and m2), and inversely proportional to the square of the distance (r) between them:

    F = G \frac{m_1 m_2}{r^2}.

Ok, now use your equation to calculate the force between the sun and a photon.

Be a little more consistent please. In the sticky Gravity thread there is your message last where you state - Photons are massless, you can only calculate momentum.
 This equation requires both bodies mass, in your case sun and photon. So, are you stating now that photons have mass?

No, he is proving that the Newtonian equation becomes invalid in explaining the world events, due to its inconsistency with some phenomenons. For example, gravitational lensing.

No, he is proving that the Newtonian equation becomes invalid in explaining the world events, due to its inconsistency with some phenomenons. For example, gravitational lensing.

Just how does he proves that when he requires to calculate something which needs mass and provides one component of equation without mass?

Just how does he proves that when he requires to calculate something which needs mass and provides one component of equation without mass?

He isn't requiring anything. He knows photons are massless, and the law of universal gravitation cannot solve for massless particles. That's why he is asking for a value as a way to prove the person, who brought up the equation earlier, wrong. Get the point?

Quote from: zork on August 24, 2008, 02:37:56 AM

Just how does he proves that when he requires to calculate something which needs mass and provides one component of equation without mass?

He isn't requiring anything. He knows photons are massless, and the law of universal gravitation cannot solve for massless particles. That's why he is asking for a value as a way to prove the person, who brought up the equation earlier, wrong. Get the point?

Yes, he requires to calculate something with formula which isn't meant to calculate it. Formula quite simply states that two masses are needed. And photon doesn't have mass as he itself says. It's like I give you the only one object and require you to calculate gravitational attraction between this one object and nothing. So, no I don't get the point.