# Novice questions about the Big Bang theory (pt. 2)

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#### falkor

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1) Why does the moon orbit the earth?<br />If gravity attracts 2 objects like the earth and the moon then why don't they crash into each other like humans would crash into the surface of the earth if running out of a helicopter?<br />I've tried the bowling ball/sheet experiment. I roll a tennis ball towards the bowling ball; it either immediately crashes into the bowling ball if my aim was perfect, otherwise it takes a small spin around the bowling ball before inevitably crashing. I've visited every website I can find about General/Special Relativity and Warped Space-Time, but none of them seem to explain it properly (neither does Hawking's book).<br /><br />2) As an astronaut is lifted away from the earth's surface does the pull of gravity have the same value whilst inside the earth's atmosphere? Once the astronaut is outside of the atmosphere why does he suddenly experience weightlessness and is no longer being pulled towards the earth? Or is all this a gradual process? <br /><br />3) One of the four forces of nature includes Electro-magnetism, but isn't electricity and magnetism both separate forces in their own right, albeit unified with mathematical equations? So instead of 4, shouldn't there really be 5 forces in total?

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#### MeteorWayne

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Using the rubber sheet analogy, you have to direct the small ball into an orbit around the larger one. If you do it perfect (and there was no friction, as in space) it will keep going around and around. If it's spiraling in, you tried to send it into orbit too slowly.<br /><br />Do a google search on orbits.<br /><br />For example, for low earth orbit, where the ISS is, it's a little over 17,000 mph parallel to the earths surface.<br /><br />As for weightlessless, the atmosphere has nothing to do with it.<br />Once you are going the proper speed for the orbit you are in, you are falling toward the earth at exactly the same speed that the surface of the earth drops away due to it's curvature. Since you stay at a constant height over the surface, you "appear" weightless. Technically, the environment is called microgravity, since you are not truely weightless.<br /><br />Why are elctricity and magnetism one force?<br /><br />Rather a philosophical question. The fact is, they are one force. It's just the rules of the Universe.<br /><br />Wayne <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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#### falkor

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Cheers mate! You've explained the first part surprisingly well providing I've understood correctly, even though I had previously Googled everything to do with "relativty", "gravity" and "orbits"; you're telling me that the sheet/ball experiment needs to be done perfectly in a vacuum then the small ball will continue circling the big ball without crashing into it?<br /><br />Next question: <br />4) Why are the planets in orbit around the sun at different distances? It obviously has nothing to do with each planet's mass?

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#### MeteorWayne

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Even in a vaccuum, there would still be friction between the ball and sheet, so you can only "stretch" the analogy so far, but without friction, with the right speed it would work that way<br /><br />Regarding orbital distances, it has to do with their obital speed.<br />To go back to the rubber sheet, if you want to orbit the small object close to the big ball, you have to roll it very fast.<br /><br />If you want a larger orbit, you have to go slower or it will just head off into space, since the sheet is bent less.<br /><br />Here's a list of average orbit speeds for the planets.<br /><br />Mean Orbital Velocity - Planets in Solar System <br />Planet ...... km/sec .... km/min ...... km/hr ....... mi/hr <br />Mercury....... 47.9.... 2,872.8... 172,368.0 .... 107,040.5 <br />Venus ....... 35.0.... 2,101.2... 126,072.0 ....... 78,290.7 <br />Earth......... 29.8.... 1,787.4 ... 107,244.0 ...... 66,598.5 <br />Mars......... 24.1.... 1,447.8..... 86,868.0 ...... 53,945.0 <br />Jupiter...... 13.1...... 784.2..... 47,052.0 ....... 29,219.0 <br />Saturn...... 9.7...... 580.2..... 34,812.0 ...... 21,618.3 <br />Uranus..... 6.8...... 408.6 ..... 24,516.0 ...... 15,224.4 <br />Neptune... 5.5 ....... 327.0 ..... 19,620.0 ...... 12,184.0 <br />Pluto......... 4.7 ...... 284.4 ..... 17,064.0 ...... 10,596.7 <br /><br />You can see, the closer to the sun you are, the faster you have to go to stay in orbit. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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#### bobw

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There is a lot of friction with a sheet, bowling ball and tennis ball. Have you ever seen one of those things you put coins into for charity and they go around and around? I am always surprised how long the coin keeps going. The surface of them is the same shape as the one you would get with a heavy weight on an ideal sheet.<br /><br />http://www.exploratorium.edu/xref/exhibits/gravity_well.html<br />http://www.funnelworks.com/design.html<br />http://www.bhmvending.com/Amusements/Impulse%20Industries/impulse_CoinFunnel_Kepler.html<br />http://www.spiralwishingwells.com/ <div class="Discussion_UserSignature"> </div>

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#### falkor

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<blockquote><font class="small">In reply to:</font><hr /><p>As for weightlessless, the atmosphere has nothing to do with it. <br />Once you are going the proper speed for the orbit you are in, you are falling toward the earth at exactly the same speed that the surface of the earth drops away due to it's curvature. Since you stay at a constant height over the surface, you "appear" weightless. Technically, the environment is called microgravity, since you are not truely weightless.<p><hr /></p></p></blockquote> <br />Sorry, I don't understand... Surely the difference between orbiting the earth and having your feet pulled to the ground has got to do with whether there is any air resistance, ie. inside the atmosphere we are being pulled towards the earth, but outside we would be pulled around it?<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Why are elctricity and magnetism one force? <br /><br />Rather a philosophical question. The fact is, they are one force. It's just the rules of the Universe.<p><hr /></p></p></blockquote><br />Not a philosophical question... Before these two were united by equations, they must have been described as two separate forces of the universe? Electricity doesn't seem to attract anything, but can kills us, whereas magnets attract metal but don't hurt us. Are you sure they are exactly the same force? <br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>You can see, the closer to the sun you are, the faster you have to go to stay in orbit.<p><hr /></p></p></blockquote><br />Ah, but the planets aren't having to work to keep up with their orbits, are they? If a spaceship was to go in orbit around a planet or moon then would it's orbital distance depend on what speed and angle it initially approached the side? Have I got that right? Anyway, thanks for posting that chart and explaining things!

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#### MeteorWayne

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<font color="yellow">"Sorry, I don't understand... Surely the difference between orbiting the earth and having your feet pulled to the ground has got to do with whether there is any air resistance, ie. inside the atmosphere we are being pulled towards the earth, but outside we would be pulled around it? "</font><br /><br />Nope, not at all. The only thing that determines whether you orbit or fall to the ground is how fast you are traveling parallel to the surface. When you are traveling at a speed where your rate of fall (which is constant; 32 ft per second per second) equals how fast the surface curves away, you are in orbit. If you are going slower, you fall to the ground. If you are going faster; it's earth in your rear view mirror <img src="/images/icons/smile.gif" /><br /><br />The effect of the atmosphere is to provide friction, so if you are in the atmoshere, you need to apply more energy to keep a constant speed to stay in orbit. Even where the ISS is, there is enough atmosphere that it has to be boosted once in a while to keep it's speed up.<br /><br /> ISS height chart <br /><br /><font color="yellow">"Ah, but the planets aren't having to work to keep up with their orbits, are they? If a spaceship was to go in orbit around a planet or moon then would it's orbital distance depend on what speed and angle it initially approached the side? Have I got that right? "</font><br /><br />That's correct. As long as you don't get slowed down by interactions with an atmosphere or moon (or some other force), you orbit forever.<br /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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#### falkor

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Thanks Wayne! So if we slowed the Moon down enough would it crash into us? Isn't the Moon a bit of a hazard for us? What if it got hit by a big asteroid? Another thing... our 365 day orbit has never been disturbed by anything during human history?

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#### MeteorWayne

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"So if we slowed the Moon down enough would it crash into us? Isn't the Moon a bit of a hazard for us? What if it got hit by a big asteroid? Another thing... our 365 day orbit has never been disturbed by anything during human history? "<br /><br />Yes, if the moon slowed down substantially it would crash into the earth,<br />That would be bad!!!! Even a huge asteroid would have little effect on it's velocity since asteroids are very very very very small compared to the moon.<br /><br />All the asteroids there are together in the asteroid belt are less mass than the moon.<br /><br />BTW, our orbit is currently about 365.24 days. <img src="/images/icons/smile.gif" /> That's why we have leap years, to keep the calendar in time with the orbit....that extra quarter day makes a full day every 4 years so we add a day to February every 4 years to tidy things up.<br /><br />In actuality, the year is getting longer but the number of days in a year is decreasing, but both occur at VERY long time scales. I mean REALLY long.<br /><br />The sun is losing mass (the solar wind sending stuff into space) so our obit is very slowly getting bigger. And the earth's rotation (day)is getting longer (due to the interaction of the Moon and tides on earth) and the moon is slowly moving away as well. <br /><br />Over billions of years, these will become noticeable. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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#### falkor

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OK thanks again Wayne! It's seems you've already thought about all these potential problems.<br /><br />The 3rd question still remains... I heard that the Weak Nuclear Force has been unified with another force, but yet it's still identified as a separate force, so why isn't electricity and magnetism listed as seperate elementary forces?

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#### MeteorWayne

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Briefly, because electromagnetism is one force. It operates over the same distance scales, and can easily be converted from one to the other, because they are dirrerent views of the same force.<br />I'm still searching for the right works to try and make it clearer.<br />When I do, you'll be the first to know <img src="/images/icons/smile.gif" /><br /><br />The other forces, the strong and weak nuclear forces, operate on vastly different, but atomic distance scales, and with different strengths and charachteristics, wheras EM covers the length of the whole universe.<br /><br />MW <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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