|
|
Post by abacus9900 on Sept 6, 2010 16:00:36 GMT 1
Why is it that two objects of different weights arrive at the ground at the same time when dropped from a tall building? The heavier object should reach the ground first, but does not.
|
|
|
|
Post by trollhunterx on Sept 6, 2010 16:28:50 GMT 1
The heavier object should reach the ground first If I wanted to be awkward, I'd say, 'why?' If I wanted to be really awkward, I'd say, 'That's just IPCC propaganda!!' But I'll just say that all objects accelerate towards the ground at the same rate, regardless of their weight, unless wind resistance becomes an issue. Galileo proved that (or was it Voltaire?) |
|
|
|
Post by abacus9900 on Sept 6, 2010 16:35:33 GMT 1
So what is weight then joe?
|
|
|
|
Post by speakertoanimals on Sept 6, 2010 16:45:49 GMT 1
F=ma
And since inertial mass m is proportional to weight, that is why all objects fall the same (ignoring air resistance).
It is actually a big problem for Newtonian physics why the gravitational mass (which determines the weight) should be EXACTLY the same as the inertial mass. Seems to be a lucky coincidence, with no deep explanation as to why.
Except in general relativity, the reason why all objects fall the same is not some lucky equivalence of masses, but because they are all moving in the same curved spacetime -- there are no gravitational forces, just the effects of curvature. We only think there are forces if we pretend that space and time are flat, just as we only think there are centrifugal forces on a spinning roundabout.
Hence the act of dropping a feather and a hammer on the moon leads to a totally different picture of what space and time are actually like, and also leads to the fact that the universe should be expanding (although einstein missed the chance to predict that, because everyone at the time thought it was static, so he fudged it!).
A seemingly uninteresting effect that turns out to have big consequences.
|
|
|
|
Post by helen on Sept 6, 2010 16:49:10 GMT 1
|
|
|
|
Post by trollhunterx on Sept 6, 2010 17:04:04 GMT 1
So what is weight then joe? Typical Warmist deflection... regardless of their weight |
|
|
|
Post by abacus9900 on Sept 6, 2010 17:36:21 GMT 1
Aha! So F=ma describes weight. So weight is really a force? Right, so if I understand you, weight is really a measure of force and the way objects fall is a result of them following the curvature of space. Fantastic.  |
|
|
|
Post by abacus9900 on Sept 6, 2010 17:41:33 GMT 1
Thanks Helen. Yes, that makes it obvious that it is the gravitational field that acts on the acceleration of objects. Change the gravitational field and you change the accelerations rate, although, as Speaker has revealed, it is really the curvature of the space of a given gravitational field that acts on mass. Thank you. ;D |
|
|
|
Post by speakertoanimals on Sept 6, 2010 17:43:15 GMT 1
Weight is a force, caused by gravity, which is why you are a different weight on the moon.
If we pretend space is flat, and apply F=ma, the acceleration depends on the inertial mass m, and the force depends on the gravitational mass. That all objects have the same a in the same gravitational field say that there is some magic relation between inertial mass and gravitational mass. And experiments also show that just as inertial mass doesn't depend on the exact substance (a kilo of lead compared to a kilo of water), so for gravitational mass.
Einstein -- all objects fall the same because they are moving in the same curved spacetime, because it is the curvature of spacetime that is gravity. Same spacetime, same fall.
|
|
|
|
Post by trollhunterx on Sept 6, 2010 17:55:30 GMT 1
|
|
|
|
Post by abacus9900 on Sept 6, 2010 18:29:07 GMT 1
Einstein -- all objects fall the same because they are moving in the same curved spacetime, because it is the curvature of spacetime that is gravity. Same spacetime, same fall. Wait a minute, the mass of the body must have something to do with the way space is curved because things fall at different rates on the earth as compared to the moon. This means the earth curves space more than the moon, doesn't it? |
|
|
|
Post by Progenitor A on Sept 6, 2010 18:34:10 GMT 1
Einstein -- all objects fall the same because they are moving in the same curved spacetime, because it is the curvature of spacetime that is gravity. Same spacetime, same fall. Wait a minute, the mass of the body must have something to do with the way space is curved because things fall at different rates on the earth as compared to the moon. This means the earth curves space more than the moon, doesn't it? Ah yes! Does space-time curve in the ABSENCE of matter? Or is matter the cause of space-time curvature? So is space-time is only curved when matter is present, then what does space-time curvature tell us that the laws of gravity do not? |
|
|
|
Post by abacus9900 on Sept 6, 2010 19:34:12 GMT 1
naymissus, it is my understanding that in the absence of matter space would be flat.
|
|
|
|
Post by Progenitor A on Sept 6, 2010 19:53:20 GMT 1
naymissus, it is my understanding that in the absence of matter space would be flat. OK, so if S-T is only curved in the presence of matter, resulting in 'gravitational' effects, then what does S-T curvature add to Newton's Theory of Gravity? |
|
|
|
Post by abacus9900 on Sept 7, 2010 8:16:55 GMT 1
Your questions are very searching naymissus and I am no expert but I think we have to remember that Newton's ideas were just a very good approximation of the way S-T works and it would be more pertinent to ask the same question in regard to Einstein's ideas. Perhaps Speaker_To_Animals could comment on this as she is a professional physicist.
|
|
