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Gravity is Bunk!!!

Another thread that changed my life. I actually enrolled in a physics class at my local community college, but had the crappiest prof. ever. More interested in pushing his bands next gig than teaching. I aced the class but so did everyone, and I'm sure it resulted from him "mailing it in" that semester. I just got accepted to a university last semester for my final two years of undergrad, so I was thinking of retaking it or taking a similar class as one of my last elective courses.

Also, reading a book from Isaac Asimov called Understanding Physics, but I'm having trouble visualizing exactly how gravity works. Honestly, I'm feeling a little overwhelmed by this book. Does anyone have any suggestions that could help me out?
 
I think King Merv was the person who came closest to understanding my question. His interpretation IIRC was "what causes gravity" and I believe he said it was just theory at this point, but I was just hoping to get a visual of what keeps us on this big "tennis ball" of a planet?
 
This is part of Carl Sagan's Cosmos. 3:05 onwards explains gravity.
 
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Just watched it 3 times. Very, very cool.

Questions:
1) So in that visual, we (earth) are the moving (revolving) ball, and stationary ball is the sun?
2) The mass of the planet decides the depth of the "pucker" it rests in?
 
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I think green energy like wind and wave energy is dangerous to the survival of all life on earth. If we managed to extract all wave and wind energy available to us, the eath stop spinning and we would all be squished by the relative increase in gravity. Pretty bad situtation if you ask me. You heard it here first.

:jaw-dropp
 
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Wow, I felt a brain-wrinkle form. It's like this feeling you get when you're on the verge of kinda understanding something, lol!

Questions:
1) So on a lesser scale, the Moon (revolving body) and earth (stationary) have the same relationship, but Earths got a smaller "pucker?"

2) Will these revolutions eventually get smaller and smaller until we hit the sun (hypothetically), or is the some force acting on the revolving body that prevents this?
 
DaN K. StAnLeY said:
Wow, I felt a brain-wrinkle form. It's like this feeling you get when you're on the verge of kinda understanding something, lol!

Questions:
1) So on a lesser scale, the Moon (revolving body) and earth (stationary) have the same relationship, but Earths got a smaller "pucker?"

2) Will these revolutions eventually get smaller and smaller until we hit the sun (hypothetically), or is the some force acting on the revolving body that prevents this?
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1) No, actually when considering the Earth and the moon, the moon has the smaller pucker. The size of the pucker, meaning the strength of its gravity, is directly proportional to the body's mass. The Earth has the larger one compared to the moon, but it is smaller than the sun's, and so on. You also have to understand, intellectually, that the grid with the pucker is really a 3D grid with a similar 3D pucker, and is simplified for ease of understanding, though trying to visualize that is a little more difficult. The pucker exists in 3 dimensions, so it attracts above and below the planets as well as around it.

2) If you only have two bodies, then, no, the orbits around each other are stable and will last forever. When you start bringing in other forces, though, like another body, or dust/gas clouds or atmospheres which impinge on one of the bodies, their orbits decay and result ultimately in merging. The point in the two body solution is that there are no other forces involved besides momentum and gravity; when you start bringing in other things there are gravitational perturbations and friction with other objects which cause and energy exchange (takes momentum out of the object and heats up the cloud a little).

The thing about the moon's orbit moving outwards is just such an interaction which takes energy out of the Earth's spin and transfers it to the moon, increasing its angular momentum and thus its distance from Earth. Ideally, it will continue until there is no more rotation of the Earth with respect to the moon to transfer. That'll take a long time, like 50 billion years, to happen.
 
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Something that I've found that there is lots of confusion about is point sources of gravity. When you are making a computation about the effects of gravity on two or more masses, it is often convenient to treat the bodies as if they are points located at the bodies' centers (more precisely, 'centers of gravity') with the same mass as the body. As long as all calculated positions are outside the bodies real extent, then this works fine. Orbital simulators do this routinely. The problem happens when interaction might get the bodies too close together and the simulation never checks for it; the collision that results in real life is never seen in the sim.

A black hole *really is* a point source of gravity; the gravity has gotten so high in so small a space that the structure of the matter cannot withstand being sucked closer and closer until all the mass is concentrated in a geometrical point in space - infinite density, a singularity. People have a vision of a black hole being a ravenous maw that sucks everything in, but it is no more that than a star of the same mass. People understand (thanks to Star Trek, mostly, I think) that one can safely orbit a star, but they see the equivalent black hole as sucking them in (and I blame a lot of video documentary graphics for that). If the sun suddenly converted its matter into a black hole, it would get real dark and cold, but we and all the rest of the planets, asteroids and trans-neptunian objects would just continue orbiting it just as if nothing had happened.
 
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DaN K. StAnLeY said:
Also, reading a book from Isaac Asimov called Understanding Physics, but I'm having trouble visualizing exactly how gravity works. Honestly, I'm feeling a little overwhelmed by this book. Does anyone have any suggestions that could help me out?
Click to expand...

Somebody wrote a book called "The attractive Universe". I think I have it somewhere, but try Amazon. I'm pretty sure it was published by Doubleday, can't recall the author. However, it explains, Asimov-style, how gravity functions and is applied.

...

No it wasn't Doubleday, but the author is Valens. Here:

http://www.amazon.com/Attractive-Universe-Gravity-Shape-Space/dp/B000JC3JFW

Hans
 
BadBoy said:
I think green energy like wind and wave energy is dangerous to the survival of all life on earth. If we managed to extract all wave and wind energy available to us, the eath stop spinning and we would all be squished by the relative increase in gravity. Pretty bad situtation if you ask me. You heard it here first.

:jaw-dropp
Click to expand...

Just in case you are serious: All this stuff does, directly or indirectly, tap into Earth's rotational energy, and eventually Earth WILL stop and always face the same side to the sun. :eek:

The good news are:

1) This will take billions of years. Mankind will be long gone for other reasons by that time.

2) It will happen no matter what we do and it will not happen faster because we use some of the energy for our own purposes, it will just be lost otherwise. :p

Hans
 
shadron said:
2) If you only have two bodies, then, no, the orbits around each other are stable and will last forever.
Click to expand...

That's true in Newtonian gravity, but not in general relativity. Even just two bodies orbiting will radiate energy in the form of gravity waves. As a result, they will eventually spiral in and collide. The increase in orbital period during this process has actually been observed in binary pulsars, and it's one of the few pieces of evidence we have for gravity waves.

shadron said:
A black hole *really is* a point source of gravity; the gravity has gotten so high in so small a space that the structure of the matter cannot withstand being sucked closer and closer until all the mass is concentrated in a geometrical point in space - infinite density, a singularity.
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That's not really correct. Black holes have horizons with finite radius, and it's best to think of the horizon as defining the size of the hole. For example the horizon can oscillate, radiate energy, deform in overall shape. It even has an electrical conductivity, not that you're going to be able to measure it. In many ways it behaves like a surface.
 
MRC_Hans said:
Just in case you are serious: All this stuff does, directly or indirectly, tap into Earth's rotational energy, and eventually Earth WILL stop and always face the same side to the sun. :eek:

The good news are:

1) This will take billions of years. Mankind will be long gone for other reasons by that time.

2) It will happen no matter what we do and it will not happen faster because we use some of the energy for our own purposes, it will just be lost otherwise. :p

Hans
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lol.

Maybe if we all run in the same direction we could speed up the earths rotation, put some sping back into it ;)
 
No, actually when considering the Earth and the moon, the moon has the smaller pucker.
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Sorry, i meant the earth's "pucker" is smaller than the sun's, not the moon's. Should've made myself more clear.

This thread is blowin my mind-grapes. This stuff is amazing and I really need to get into another intro to physics class. Hopefully I can get a good prof this time.
 
DaN K. StAnLeY said:
Sorry, i meant the earth's "pucker" is smaller than the sun's, not the moon's. Should've made myself more clear.

This thread is blowin my mind-grapes. This stuff is amazing and I really need to get into another intro to physics class. Hopefully I can get a good prof this time.
Click to expand...
That is how I read it and didn't notice that the words weren't right. :)
 
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