Clarification on Gravity

Why would you come to that conclusion?

The normal force would be in the up direction. 

Quote from: sokarul on September 16, 2008, 05:04:40 PM

Why would you come to that conclusion?

Quote from: sokarul on September 15, 2008, 10:34:15 PM

The normal force would be in the up direction. 

So the acceleration from gravitation went where?  So the object stays put how? 

Quote from: sokarul on September 16, 2008, 05:06:32 PM

So the acceleration from gravitation went where?  So the object stays put how? 

There is no acceleration from gravitation, and the object doesn't stay put. That is why an object on the surface of the Earth is in a non-inertial frame of reference; it is accelerating.

Of course, so when I drop a pen, it floats in the air. 

Why would you come to that conclusion?

Quote from: sokarul on September 16, 2008, 05:08:36 PM

Of course, so when I drop a pen, it floats in the air. 

Quote from: sokarul on September 16, 2008, 05:04:40 PM

Why would you come to that conclusion?

Quote from: sokarul on September 16, 2008, 05:06:32 PM

So the acceleration from gravitation went where?  So the object stays put how? 

There is no acceleration from gravitation, and the object doesn't stay put. That is why an object on the surface of the Earth is in a non-inertial frame of reference; it is accelerating.

There is no acceleration from gravitation, and the object doesn't stay put. That is why an object on the surface of the Earth is in a non-inertial frame of reference; it is accelerating.

Quote from: E.Jack on September 15, 2008, 09:51:37 PM

Make up your mind.  One minute the earth's surface is non-inertial, the next minute it is. 

Time dilation helps to show who has accelerated.  Care to take a stab as to what it shows?

Quote from: sokarul on September 16, 2008, 05:16:29 PM

Make up your mind.  One minute the earth's surface is non-inertial, the next minute it is. 

I never said it was inertial.

A guy sitting in a chair is in free-fall.

Time dilation helps to show who has accelerated.  Care to take a stab as to what it shows?

Or people are accelerated from gravitation. 

Quote from: sokarul on September 16, 2008, 05:32:33 PM

Or people are accelerated from gravitation. 

Then why would an object close to the event horizon of a black hole appear to barely move?

Because it's time dilated and there is also length contraction. 

GR doesn't require a force to accelerate an object. 

Quote from: sokarul on September 16, 2008, 05:38:45 PM

Because it's time dilated and there is also length contraction. 

But if the person falling into the gravitational well was really accelerating, wouldn't they start moving faster and not slower?

Quote from: sokarul on September 16, 2008, 04:48:46 PM

GR doesn't require a force to accelerate an object. 

Of course it doesn't, that's why we don't need gravity. The direction of force in the diagram is up, so the direction of acceleration is up. We are always undergoing a constant upward physical acceleration, according to general relativity.

End of story.

Moving clocks tick slower.

If acceleration was up, why does the object stay on the surface? 

If acceleration was up, why does the object stay on the surface? 

If acceleration was up, why does the object stay on the surface? 

Someone should make some kind of principle to that eff...

Brilliant!  But what shall we call it?  Gravity and acceleration are equivalent, so... I've got it!  We shall call it the... nevermind, I lost it.

I've got it.   Equivalentarianistical Participle!  What da ya think?

Quote from: sokarul on September 16, 2008, 08:20:43 PM

Moving clocks tick slower.

They do, but they don't appear to move slower.

Because the surface is also accelerating up.

Because if there was no upwards acceleration provided by a normal contact force the object would be burrowing downwards into the ground.  This is true in FE or RE. Acceleration and gravity are equivalent.

Someone should make some kind of principle to that eff... ahh, dammit... 100 years too late.

I have no doubt there is upwards acceleration from the normal force, but the objects net coordinate acceleration is zero. 

And BTW acceleration and gravitation are only equivalent locally.   

I have no doubt there is upwards acceleration from the normal force, but the objects net coordinate acceleration is zero.   And BTW acceleration and gravitation are only equivalent locally.   

I agree that the person standing on the ground does not move relative to the ground, but they still feel like they're being pushed upwards by the ground. 

At no point does anyone feel like they're being pulled down by the ground/Earth beneath it (insomuch as at no point will an accelerometer give you a negative reading due to gravitational attraction, where positive is defined as 'up' - the lowest it will ever read is zero, which it will do when in free fall).

As for the equivalence principle being a local axiom only - fair point, but you're not going to notice any difference on a human scale without either ridiculously accurate accelerometers or massive tidal forces (such as near an event horizon). Neither of those conditions have been specified for this discussion.

Quote from: sokarul on September 17, 2008, 07:40:02 AM

I have no doubt there is upwards acceleration from the normal force, but the objects net coordinate acceleration is zero.

Right, coordinate acceleration. The object's physical acceleration is upward. Glad we finally cleared that.

So? That still doesn't disprove why they are different.

Please research before you post again. 

Unless you are not local. 

Quote from: Osama  bin Laden on September 16, 2008, 08:24:39 PM

Quote from: sokarul on September 16, 2008, 08:20:43 PM

Moving clocks tick slower.

They do, but they don't appear to move slower.

http://www.astrophysicsspectator.com/topics/generalrelativity/BlackHoleEventHorizon.html

Quote

Because the surface is also accelerating up.

I don't argue for the FET.
Way to ignore the rest.

And the ground feels like it's being pushed down by the person. 

The normal force is present because of contact.  Look up normal force and see how it arises.  As for the accelerometer gravitation accelerates objects without a force.

...

I know, I just thought we were having a state the obvious contest. 

But don't just take my word for it:

Quote from: http://en.wikipedia.org/wiki/Equivalence_principle

In the physics of relativity, the equivalence principle refers to several related concepts dealing with the equivalence of gravitational and inertial mass, and to Albert Einstein's assertion that the gravitational "force" as experienced locally while standing on a massive body (such as the Earth) is actually the same as the pseudo-force experienced by an observer in a non-inertial (accelerated) frame of reference.

Quote from: http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/grel.html

Experiments performed in a uniformly accelerating reference frame with acceleration a are indistinguishable from the same experiments performed in a non-accelerating reference frame which is situated in a gravitational field where the acceleration of gravity = g = -a = intensity of gravity field.

Quote from: Albert Einstein, quoted in 'Gravity' by James B. Hartle

"Then occurred to me the happiest thought of my life, in the following form. The gravitational field has only a relative existence... Because for an observer falling freely from the roof of a house there exists - at least in his immediate surroundings - no gravitational field....(in this consideration air resistance is, of course, ignored)."