# gravity

eatmybishop
Posers and Puzzles 25 Aug '07 15:43
1. 25 Aug '07 15:43
forgive my ignorance on this one, but two questions about gravity which i hope someone can answer, if the gravitational pull from the sun keeps the nine planets in their orbit, why don't they just race toward the sun, whats pulling from the other side? also, how can a comet pass through our solar system without bring pulled in by the sun's gravity, if gravity has the power to hold a planet, why not a comet? thanks
2. 25 Aug '07 17:33
Originally posted by eatmybishop
forgive my ignorance on this one, but two questions about gravity which i hope someone can answer, if the gravitational pull from the sun keeps the nine planets in their orbit, why don't they just race toward the sun, whats pulling from the other side? also, how can a comet pass through our solar system without bring pulled in by the sun's gravity, if gravity has the power to hold a planet, why not a comet? thanks
Imagine a ball at the end of a string. If you swing the string around, the ball will "orbit" you. Why doesn't it fly away? Because the string pulls it towards you. Why doesn't it just go right for you then? Because it has momentum that keeps it moving sideways as well.

You can think of planets as objects that are always falling towards the sun, but just keep missing. If you managed to stop a planet dead in its orbit and let it go, it would indeed fall right into the sun. But as it is, planets have a momentum that keeps them from falling directly towards the sun.

Many comets are bound to the sun just like planets are. Unlike planets, though, they have very stretched-out elliptical orbits that take them far beyond the orbit of Pluto before they fall back towards the sun again. But there are objects that pass through the solar system without being caught by the sun's gravity. They can do this because they are moving quickly enough to escape the sun's gravitational pull.

Imagine the ball-and-string again: if you spin the ball around fast enough, eventually the string will break and the ball will fly off. An inexact analogy, but I think it conveys the general idea: to escape the sun's gravity, an object has to be moving away from it at a certain speed. But gravity is not like a string that suddenly snaps. It's more like an elastic cord, with the difference that the closer an object is to the sun, the more strongly it is pulled in, whereas with an elastic cord the force becomes stronger as the distance becomes larger.
3. 25 Aug '07 20:281 edit
I never understood gravity at all.

"Gravitation" is the attractive influence that all objects exert on each other, while "gravity" specifically refers to a force which all massive objects (objects with mass) are theorized to exert on each other to cause gravitation.

Source Wikipedia (http://en.wikipedia.org/wiki/Gravity).

Lets take two objects of different size.
Lets say an apple and a paperclip.
Now we will put those somewhere in the universe where there is no influence from anything else besides those two objects. (So it must be far enough away from planets, stars, etc).

If the distance between the 2 objects is small enough then the paperclip WILL go towards the apple. It will not stay away from it / it will not go away from it.

While I can learn that this is the truth, I simply cannot understand why.
4. 25 Aug '07 21:401 edit
Originally posted by MetBierOp
While I can learn that this is the truth, I simply cannot understand why.
Same feelings show up after a beer session. People tell you what have you done. You can accept the truth but simply cannot understand it.
Baby Gauss
26 Aug '07 11:33
Originally posted by MetBierOp
While I can learn that this is the truth, I simply cannot understand why.
Nobody else understands why too. At this moment serious gravitation theories are more descriptive than explanatory.
6. 26 Aug '07 13:39
Originally posted by GregM
Imagine a ball at the end of a string. If you swing the string around, the ball will "orbit" you. Why doesn't it fly away? Because the string pulls it towards you. Why doesn't it just go right for you then? Because it has momentum that keeps it moving sideways as well.

You can think of planets as objects that are always falling towards the sun, but just kee ...[text shortened]... whereas with an elastic cord the force becomes stronger as the distance becomes larger.
yeah, that makes perfect sense, thanks
7. smw6869
Granny
02 Sep '07 02:26
Originally posted by GregM
Imagine a ball at the end of a string. If you swing the string around, the ball will "orbit" you. Why doesn't it fly away? Because the string pulls it towards you. Why doesn't it just go right for you then? Because it has momentum that keeps it moving sideways as well.

You can think of planets as objects that are always falling towards the sun, but just kee ...[text shortened]... whereas with an elastic cord the force becomes stronger as the distance becomes larger.
More scientific mumbo jumbo. There's No gravity. There's only UP and DOWN. Did you ever trip and roll UP a stair case? No, but it's easey to roll DOWN the stairs, because one way is UP and the other is DOWN, depending where you are standing. Pure Logic!
8. AThousandYoung
All My Soldiers...
02 Sep '07 08:034 edits
Originally posted by smw6869
More scientific mumbo jumbo. There's No gravity. There's only UP and DOWN. Did you ever trip and roll UP a stair case? No, but it's easey to roll DOWN the stairs, because one way is UP and the other is DOWN, depending where you are standing. Pure Logic!
I know what you’re thinking about, but it isn’t so, nohow.

Contrariwise, if it was so, it might be; and if it were so, it would be; but as it isn’t, it ain’t.

That’s logic.
9. sonhouse
Fast and Curious
07 Sep '07 16:154 edits
Originally posted by MetBierOp
I never understood gravity at all.

"Gravitation" is the attractive influence that all objects exert on each other, while "gravity" specifically refers to a force which all massive objects (objects with mass) are theorized to exert on each other to cause gravitation.

Source Wikipedia (http://en.wikipedia.org/wiki/Gravity).

Lets take two objects of ...[text shortened]... o away from it.

While I can learn that this is the truth, I simply cannot understand why.
Picture the apple and the paper clip sitting on a thin rubber sheet, the sheet bends from the mass of the apple, right? The apple would poke a hole in the sheet if the apple was heavy enough, right. So consider the in-between, where it does not poke a hole but makes a depression in the sheet. So the paper clip is close to the apple and therefore on a part of the rubber sheet that is curved. So the paper clip slides to the apple. That is a 2 dimensional analogy of gravity. Of course you have to extend that into 4 dimensions but that rubber sheet gives you a rough idea. Gravity is a bending of space caused by mass and the rubber sheet stands in for that bending of space. Even an electron has its own gravity field, it bends space nearby a very very tiny amount. Of course electric and magnetic forces totally overwhelm gravity but it is still there, the difference in an electron is the electric charge, negative in the case of an electron will totally overpower the tiny amount of gravity or bending of space by that electron and two electrons trying to get together at non-relativistic speeds, that is, a lot slower than the speed of light, the electric fields, two negative fields, will repel each other and would never come together due to the gravitational attraction.
10. 07 Sep '07 17:53
everything has a gravitational pull the bigger the mass of the object the more pull but as the object moves away from the pulling object the pull gets weaker.

that fact plus the momentum and speed of the planets keeps them in orbit.
11. 21 Sep '07 14:00
Originally posted by eatmybishop
forgive my ignorance on this one, but two questions about gravity which i hope someone can answer, if the gravitational pull from the sun keeps the nine planets in their orbit, why don't they just race toward the sun, whats pulling from the other side? also, how can a comet pass through our solar system without bring pulled in by the sun's gravity, if gravity has the power to hold a planet, why not a comet? thanks
Because they happen to have a velocity that's constantly trying to take them away from the sun. At the present time you see the system in equilibrium. In the beggining LOTS of stuff fell into the sun, and LOTS flew away from the solar system, or was attracted by planets.
The only ones that could survive were those with a velocity perpendicular to gravity from the sun (this is an approximation, just to trying to make you understand)