She did. He said she wouldn't understand, (not a good idea), which she took as a challenge!!
(Last time it was "where does energy come from", he told her to write a paper....which she did. She traced back to the Big bang and couldn't get any further, and got frustrated)
The simple sites seem to get twisted up in magnetism and the fourth dimension of time, and there it got a tad confusing.
Ok, it looks like the simple answer goes like this:
Gravity is a force pulling together all matter (which is anything you can physically touch). The more matter, the more gravity, so things that have a lot of matter such as planets and moons and stars pull more strongly.
Mass is how we measure the amount of matter in something. The more massive something is, the more of a gravitational pull it exerts. As we walk on the surface of the Earth, it pulls on us, and we pull back. But since the Earth is so much more massive than we are, the pull from us is not strong enough to move the Earth, while the pull from the Earth can make us fall flat on our faces.
In addition to depending on the amount of mass, gravity also depends on how far you are from something. This is why we are stuck to the surface of the Earth instead of being pulled off into the Sun, which has many more times the gravity of the Earth.
Gravity is a fundamental underlying force in the universe. The amount of gravity that something possesses is proportional to its mass and distance between it and another object. This relationship was first published by Sir Issac Newton. His law of universal gravitation says that the force (F) of gravitational attraction between two objects with Mass1 and Mass2 at distance D is:
F = G(mass1*mass2)/D squared.
(G is the gravitational constant, which has the same value throughout our universe.)
Einstein's theory of relativity adds to this. His theory predicted that objects with great mass deform space around them, causing light to deflect into them. That has been shown to be true. He also predicted that gravity could travel in gravity waves, which we haven't seen yet.
None of this explains why mass or distance affects gravity, though. To do that, we must look at the theories of scientists more recent than Einstein. According to theory, the reason mass is proportional to gravity is because everything with mass emits tiny particles called gravitons. These gravitons are responsible for gravitational attraction. The more mass, the more gravitons.
Graviton theory also accounts for differences in gravitational attraction over distances. Most gravitons exist in a cloud around the object. As distance from the object increases, the density of the graviton cloud goes down, so there is less gravitational attraction.
When objects are in orbit around each other, there is a strong pull of gravity between them. For example, we commonly say that the Moon is in orbit around the Earth. However, the Moon pulls back on the Earth as well. This changes the Earth a little. One way we see this happening is the ocean tides.
The amount of gravity between two objects depends on the masses of the objects, and also the distance between them. When you have two very large objects like the Moon and the Earth, different parts of them are pulled differently due to distance. The part of the Earth closest to the moon is pulled most. If there are oceans there, they will bulge out. The middle of the Earth is not pulled as strongly towards the moon, but it still is pulled more than the water on the far surface of the Earth. The far side of the Earth is pulled least, making another bulge on the far side of the Earth. As the Earth rotates underneath these bulges, we experience two high tides per day.
I would babble that;-
Everything is a collection of wavelegths and vibrations, we percieve this as solid. That they are in a constant state of vibration means they are cyclic and return their own energy from themselves, this then creates perceptible matter and density. It is density that creates gravity.
I am not sure if the constant referred to by einstein is the same as that which determines the rotational speed of a planet or its arc around a star etc ? it was a long time ago since I pondered on the maths of the universe.
If the Earth was twice as big would a day be 48 hours long but the year only 182.5 days long... I honestly can't remember, but there are percievable constants in the universe. Universal ratios.
"How will you keep the humans on the Earth" said lucifer to Jove, "they'll sureley leave than be indebted to your creation?"
Jove pondered and declared, "I'll spin the Earth so bloody fast they'll be too dizzy to wonder how to get off!" _________________ ---
Ooooooh, thanks Samjaza, you just reminded me of something, nearly. Something that i think I used to know. It'll come....... (don't you just hate that little nagging feeling in the back of your mind that you can't quite put your finger on) ....lurches off to find a book.......
short version. every bit of mass no matter how small atracts other bits of matter. the more mater the more pulling power or gravity it has.
Imagine a bed sheet (space) stretched really tightly. put a snooker ball in the middle to represent the sun. then roll another snokker balll around the sun. The ball you roll round will begin to fall into the dimple the sun is making in the middle of the sheet. Thats the 2dimensional version of it, now imagine it in 3d and imagine every snooker ball isnt just making a dimple directly below it but its bending the fabric of space around its whole body. all the planets will circle it, be attracted to it, because of the dimple its causing ...its bending space. that is gravity. :)
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