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Lesson #2: Gravity
Gravity is a strange force. We're not really sure how it works, but we have a good idea.
Picture if you will, the space time continuum as a waterbed...2 dimentional, I know...but its a good analogy.
You know how waterbeds work...when something gets on one, they sort of sink and make a big ol' divit...a sort of depression.
If you were to place something on it like a bowling ball, you will get a nearly perfect cone shaped depression.
[img]http://www.zarm.uni-bremen.de/2forschung/gravi/research/EP/images/gravity_middle.jpg[/img]
So lets pretend that bowling ball is the sun. Place a smaller sphere next to it, like a marble...we'll pretent that one is the earth...and what happens?
Well it all depends on how close you put it, right? If you put the earth at the very edge of the bed, the depression made by the sun won't be big enough to cause the earth to roll into the middle.
But if you put the earth rather close, like right on the edge of the depression, it will begin to roll. First slowly, and ever faster as time goes on. Eventually it will hit the sun.
Hmmm...well that ain't a good thing if the earth burns up. Thats where I keep all my stuff. But we do want it close enough so we stay warm.
So lets give the earth some energy. We'll fling the earth JUST CLOSE ENOUGH that it will get caught in the depression and start to turn in a circular path around our bowling ball/sun. Now we have ourselves a nifty little orbit.
If you're having trouble picturing this, picture one of those giant funnel shaped 'banks' you see at the malls that ask for spare change for various charities. You put the coin in and it starts rolling down the funnel for a LONG time.
[img]http://www.ulyasutay.freeuk.com/Llandaff/halfsize/Gravity.jpg[/img]
And note that the larger the mass in orbit, the longer it takes for it to get to the middle.
But you must also realise that the larger the mass of the 'sun', the bigger the depression, thus more things can get caught within the 'Cone of NO RETURN!'.
So what happens to the earth as it hits the sun? Well it gets absorbed into that mass basically. You'd see a pile of little marbles collecting around our bowling ball.
But what would happen if the 'sun' mass was exceptionally large? Like a 5 ton safe?
Well, placing that on your waterbed will probably mean you now have a large hole in your waterbed AND the floor of your room leading into the basement.
That my friends is a good example of what black holes do. Their mass is so huge they have essentially ripped a hole in space-time that leads...well the great basement of the universe...whatever THAT is.
Thanks dude!
I do have a question though. Black holes are essentially collapsed stars or suns. So, suppose we have a sun. It's really really hot and stuff. The mass of all gases, hydrogen, etc. is being used to fuel the sun. So the mass of the sun is constantly decreasing because matter is being converted into energy, light, heat, etc. Now, if someday this sun collapses into a black hole, it would actually have less mass than it does today. Therefore, it would have less of a gravity pull than it did before as a sun.
So why are black holes such big gravity pockets/whirlpools if their mass has been decreasing before they were ever black holes?
First of all...
The mass lost to energy conversion is pretty tiny compared to its entire mass.
E = mc^2
Using this equation, just having a gram of matter (about the size of a paper clip) converted into pure energy gives you enough of an explosion to destroy...well something big. Probably along the lines of the entire state or so...I've never done the actual math on how much energy is needed to blow up the state, so I'm not sure...
But it is quite the impressive amount of energy.
Now when you factor fisson, same thing. A nuclear bomb has a baseball sized chunk of plutonium. When it blasts, a rediculously small amount of matter in converted to energy. So small we pretty much count the mass after detonation EQUAL to the pre-detonation mass.
Fusion (what our sun does) is about the same.
So yeah, a sun loses mass...but not as much as you'd think....
Secondly, remember that before suns go super-nova, they expand. They get REALLY big. Before our sun goes nova, it will have reached a size large enough to envelop the earths ORBIT.
Mass still doesn't change much...BUT lots of stars are so close to each other (believe it or not, our single sun solar system is out of the ordinary) that the big 'uns start stealing mass from the others. You might have seen pictures of stars with these big "streamers" of energy and light and plasma between them in a sort of whirlpool look.
So those stars actually start stealing mass.
Lastly, a black hole is also about AREA. Even a sun that has lost mass still has alot of mass left. When all of that is smashed into a space the size of a softball...well stuff gets all wonky.
Believe it or not, if our sun instantly became a black hole right now, the solar system wouldn't change much. From this far out, the gravitational pull is pretty much the same as it was a full sized sun.
But as you get closer, the pull of gravity gets very big at a MUCH faster rate.
So if you were flying VERY fast, you could get pretty dang close to our sun and still fly right by.
In the case of a black hole, no matter how fast you are moving, if you get that close you're toast.
What happens to something that gets sucked into a blackhole? Is it crushed into nothing?
Sorry to interject, but...
*wiggles finger mysteriously*
No one knoooooowssss...
...
...
I'm going to spend the night reading about them though. Why? Because I found a recent book 'The road to reality', the last word in that title being one I despise very much. Book talks about the 'laws' of the Universe.
[quote="Charlie"]Believe it or not, if our sun instantly became a black hole right now, the solar system wouldn't change much. From this far out, the gravitational pull is pretty much the same as it was a full sized sun.[/quote]Wouldn't change much except that we'd all need to start stocking up on candles and really warm parkas...
Great subject, Charlie!
Danka!
Speakin' of gravity, I'm reminded of that quiz question about throwing a ball in the air inside a moving train car...essentially removing the wind-resistance or what ever. Now, if I'm not mistaken, the ball would fall mostly just straight down, technically moving forward with the train, even while not attached to it. Is that right? And given enough time, like if it fell really slowly, would it drift back toward the back of the train? Would fish in a tank? Why don't they?
Very cool Charlie, I liked the way you explaind it. Its actually been said that gravity is quite weak compared to its potential strength. I don't remember the whole thing, but it states that gravity is not actually tied down to a dimension, it just floats around. If it was tied down to a dimension, it would be so much stronger. Or some thing like that. I dunno. Anywho, very cool post.
With a melon?