How satellites and children's roundabouts go round and round, faster or slower. Maybe some are interested and they can give their offspring some evil ideas. New clickers on Globalstar might be interested in orbit dyamics too. Message 11916332
Without gravity, if a satellite was fired off at high speed, it would simply zoom off never to return. It would do that even at slow speeds. You could launch stuff at 50 kph and it would just drift away, slowed by air resistance. Some of us have dreams of flying and no gravity is a wonderful feeling, though you have to watch out for power wires.
So we need to hang onto those satellites, so that they don't just zoom off forever. Maybe sometime you've been on a roundabout, usually as a kid, and usually there is a bigger kid who makes it go way to fast. What you do is hang on like crazy. If you don't, you go flying off into space.
Well, somebody invented gravity, so when satellites are zooming around flat out, they hang on to earth but don't even need a rope or anything to do it. Just the pull of gravity. So they don't go flying off into space.
So satellites just go round and round and round, hanging onto earth by gravity pulling them. Same as a kid going round and round on a roundabout, hanging on.
How hard you have to hang on, depends on how far away from the centre of the roundabout. Specifically, and to make it all proper, the force you need to hang on with = mw2r
m = how heavy you are [your mass, which is sort of how heavy you are].
w = how fast the roundabout is ripping around [rpm].
r = how far out from the centre you are.
So, little guys with low mass [m], don't need such a strong grip to hold on [which is just as well, because little guys don't have such a strong grip]. They can use a thin piece of rope to tie themselves on with. Big guys need strong ropes because their big m means they need a strong hang on.
The faster it goes, [the bigger w is] the harder it is to hang on, so the stronger the ropes need to be. You know this. You hate it when the big kids zoom the thing faster and then you fly off it out into space.
If you can get closer to the centre so you make a smaller circle as you go round and round [a smaller r], you don't have to hang on as hard either. So if you see a big guy get on the roundabout - get nearer the centre before he makes it go faster.
Now, really cunning kids can do little tricks. For example, [don't try this at home], they can make it go faster by climbing to the centre. If you get 6 buddies together on a roundabout, you all run and get it going, then jump on. Then 5 of you quickly climb to the centre, but don't tell the other guy that you are going to do that. What happens is that your angular momentum is reduced as you climb to the centre and that angular momentum gets transferred to the roundabout and your 'buddy' as you all pull yourselves to the centre. The roundabout goes faster and faster as you pull yourselves to the centre and your buddy can't hold anymore and goes flying off into space! You are okay because you are closer to the centre. It becomes a race and slow ones get biffed off too!
The faster you pull yourselves to the centre, the faster it accelerates and the less time your buddy can figure out what's happening and the less the thing slows down because of the useless bearings and wind resistance.
Of course, it can just be fun and nobody needs to get flung off.
With gravity, it's a bit different because the closer you get to earth, the stronger the rope so the faster you can go. In fact if you go too slowly, you just get pulled into the ground. Try swinging a bucket of water around and around in a vertical plane and if you go slowly the water and bucket fall down on your head. If you go fast, the water just stays in the bucket upside down even though gravity is pulling them down. Same sort of thing.
If you fire a satellite a long way away, say way out to as far as where the moon is, gravity is much weaker there, so it's pull is weak and you can go slower without falling down. In fact, you take a month to go around the earth. Same as the moon.
If you stay really close, like 1414 km, same as Globalstar satellites, you take just over 100 minutes to go round the earth because if you go slower, you fall down.
If you get really close, like 10km high, where 747s fly, you need wings because you can't go fast anyway because of all the air resistance.
Stuff like that!
So, now you know. Have fun in the playground with your kids today! Big guys [and adults] climbing to the centre transfers a LOT more angular momentum, so make sure the big kids don't know about this.
If you are twice as far from the earth's centre, the gravitational pull is quarter what it is closer. [Don't confuse the centre of the earth with how high you are - 10km high is NOT the distance from the centre of the earth and neither is 1414 km high for the Globalstar satellites].
If you go about 37,000 km high and fly around earth over the equator in the same direction it's rotating, you can stay straight over the same place all the time without falling down or zooming up if you go at just the right speed. Those are where geostationary satellites live and there are HEAPS of them. 132.163.64.201
That orbit is popular because your satellite never goes out of sight. With Globalstar, if you are talking on your Globalstar phone, the satellite you are talking to goes out of sight as it goes round the earth and another one has to come into sight before the first one disappears or the call would drop. That's why there are 48 satellites - you need that many at 1414 km high to make sure all the populated areas can see a satellite at any time.
So, there you have it.
Maurice
PS: For launching satellites, a gravity-free slow launch, such as 50 kph would be very cheap and convenient. A satellite could be lifted up to the right altitude then accelerated into the right orbit, then gravity turned back on. Happily, my invention, the Graviton Spin Reversal [TM]antigravity device is nearing prototype and investors can send me money to get a share of this amazing new technology which will revolutionize space travel as well as terrestrial travel. SurferM has an early stake [as soon as his encrypted Q cybercash arrives from cyberspace, where it seems to travel VERY slowly]. Be in soon! Send Q now. |
