Hi everybody!
I have recently begun to study physics just because it's fun. well, I am at the very begining of my studies and so I have some questions that bother me (in fact some of them drive me crazy) well, here are my questions
a) in space, the sun exerts gravitation on the earth and vice versa. if they would both have the same mass the gravition of both would be the same and would cancel each other out. but the sun has a much higher mass than the earth thus its gravitation should be higher as well, right? so, if the earth gets too close it will crash into the sun and it is too far it will leave the orbit of the sun and fly out into space. but how can there be an equilibrium (meaning that the earth can keep turning round the sun for ever)? would'nt the contrary be much more likely, so that we would observe planets leaving the orbits or crash into each other?
b) i learned that a perpetual motion machine is not possible. this comes from the law of energy conservation. when the earth is turning round the sun it is in motion because of the gravitational energy of the sun (just like a stone that somebody picks up and drop it). but somebody has to pick up the stone which "costs" energy that is transformed into potential gravitational energy that you "can get back" when you drop the stone. what is the analog of the earth? what energy is lost when the earth is turning around the sun continously? will it stop someday?
c) if you would put two tennis balls in space (just like the earth and the sun) they would attract each other. at the right distance they would move around each other. why is that not a perpetual motion machine?
d) energy is conserved which means it is transformed into some kind of other energy. the overall amount stays the same. does that mean that the whole energy in the universe is constant? it has ever been the same amount and will never change?
e) but how can the universe expand then? would'nt it be impossible for it to extend for ever? because in order to extend you need energy which come from somewhere. just like if you play pool and you hit one ball with the white ball. the force of the white ball will set the other ball into motion but the other ball will not move forever?
well, i know the answer to those questions must be simple for somebody who has an advanced understanding of physics. to me, there are just some big questions marks and i can't wait until i will have learned more about the fundamental laws of physics.
so thank's for your help