Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Karen W. on 19/07/2009 11:14:01
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Well I am curious what all holds everything in place..?
Does centrifugal force play into it with the rotation of planets etc?
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In general centrifugal force does not play any significant effect on the earth's gravity but the difference in the acceleration due to gravity is measurable quite easily and gets bigger as you approach the poles
http://www.kayelaby.npl.co.uk/general_physics/2_7/2_7_5.html
gives you the full details but you feel about half a percent heavier at the poles than the equator so if you weighed 100 pounds it would be half a pound and completely not noticeable but definitely measurable
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Hi Ian.. (In a child like voice) My name is Karen W and I am 5 years old.. I want to know what holds the stars in the sky?
Why do other planets not just fall down?
Ps.I understood nothing from the link all equations were way over my head!
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Hi Karen. Try thinking about it this way instead: "What makes things fall to Earth? I think that what it is, is that you've grown up at the bottom of a gravity well i.e. on a planet, so it seems natural for things to fall, but really the nature of things is to stay where they are, or if moving, to keep moving at a constant rate.
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The stars planets and everything else are always in effect falling down towards the nearest thing that is attracting them by gravity as gravity tries to pull them together. However they are first of all a very long way away and so would take a very long time to fall down. but more than that they are moving a bit in their own right and so they don't fall down straight but effectively miss the object that they are falling towards we call this effect an "orbit" the moon is falling towards the earth but it is moving sideways and by the time it has fallen it has moved to the side this is just the same for the earth falling towards the sun and the sun falling towards the centre of our galaxy and the other galaxies win our local group.
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OHHHHHHHHHHH ok.. I like the gravity well description....Ok like cool.. I think I get it..stars are above the gravity basically so pretty much just hang out where they are naturally shooting off occasionally and having bits blown into the force of gravity and propelled down towards Earth... ok....Thank you....
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The stars planets and everything else are always in effect falling down towards the nearest thing that is attracting them by gravity as gravity tries to pull them together. However they are first of all a very long way away and so would take a very long time to fall down. but more than that they are moving a bit in their own right and so they don't fall down straight but effectively miss the object that they are falling towards we call this effect an "orbit" the moon is falling towards the earth but it is moving sideways and by the time it has fallen it has moved to the side this is just the same for the earth falling towards the sun and the sun falling towards the centre of our galaxy and the other galaxies win our local group.
Thank you for that wonderful explanation.. You made it much easier for this gal to understand... Thank you!
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Personally. i think all the stars and planets are held up with blu tac !...it's well good at keeping stuff up !
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The concept that states gravity is pull, will confuses us. I don't know why people prefer to use the term 'pull' rather than 'push'.
Based on Kepler's Law, I develop a new understanding about gravity. It is too long to write here. Sorry I just can give you the link to my blog:
http://ian-titen.blogspot.com/2009/07/view-from-event-horizon.html
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The stars planets and everything else are always in effect falling down towards the nearest thing that is attracting them by gravity as gravity tries to pull them together. However they are first of all a very long way away and so would take a very long time to fall down. but more than that they are moving a bit in their own right and so they don't fall down straight but effectively miss the object that they are falling towards we call this effect an "orbit" the moon is falling towards the earth but it is moving sideways and by the time it has fallen it has moved to the side this is just the same for the earth falling towards the sun and the sun falling towards the centre of our galaxy and the other galaxies win our local group.
Moon does not fall to the earth because it has relative velocity with earth. OK, so what make earth does not fall to the moon? If the answer is because the earth move around the sun, why the earth does not collide with the moon when the moon heading the earth movement?
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Hi Karen. Try thinking about it this way instead: "What makes things fall to Earth? I think that what it is, is that you've grown up at the bottom of a gravity well i.e. on a planet, so it seems natural for things to fall, but really the nature of things is to stay where they are, or if moving, to keep moving at a constant rate.
Space is doing that. Sorry, I put my blog address again: http://ian-titen.blogspot.com/2009/07/view-from-event-horizon.html
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I like to look at it in terms of Energy.
If the Earth started a very long way away from the Sun ('infinity') and fell in towards it on a direct path, it would gain a certain amount of Kinetic energy (i.e. be going at a certain speed) by the time it arrived at our present distance due to it accelerating all the time it was approaching the Sun. That amount of energy is called its Gravitational Potential Energy - it is the work which is available from bringing the Earth from infinity to its orbital position. (It isn't 'quite' at the bottom of gravity well - it's 150 million km away from it)
If you could then make it 'turn sharp left', so its motion was tangential, it would go into a circular orbit- attracted to the centre but going just fast enough not to fall or to escape. Its Kinetic Energy would be exactly the same as its GPE. That's the situation for every orbit. The potential energy would be the same amount (but negative, because we got work out of the process of falling) as the KE. Its total energy would be zero.
If it didn't quite turn hard left - went off at a different angle - then its orbit would be an ellipse (which, of course, it is). The total amount of energy would still always be zero but when it was further away it would be going slower (less KE) and its PE would be less negative - still adding up to zero and vice versa when it was closer.
Rambling and confusing but interesting - total energy = zero!!
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Personally. i think all the stars and planets are held up with blu tac !...it's well good at keeping stuff up !
Is that how you attach your CDS to your walls?
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The concept that states gravity is pull, will confuses us. I don't know why people prefer to use the term 'pull' rather than 'push'.
Based on Kepler's Law, I develop a new understanding about gravity. It is too long to write here. Sorry I just can give you the link to my blog:
http://ian-titen.blogspot.com/2009/07/view-from-event-horizon.html
The stars planets and everything else are always in effect falling down towards the nearest thing that is attracting them by gravity as gravity tries to pull them together. However they are first of all a very long way away and so would take a very long time to fall down. but more than that they are moving a bit in their own right and so they don't fall down straight but effectively miss the object that they are falling towards we call this effect an "orbit" the moon is falling towards the earth but it is moving sideways and by the time it has fallen it has moved to the side this is just the same for the earth falling towards the sun and the sun falling towards the centre of our galaxy and the other galaxies win our local group.
Moon does not fall to the earth because it has relative velocity with earth. OK, so what make earth does not fall to the moon? If the answer is because the earth move around the sun, why the earth does not collide with the moon when the moon heading the earth movement?
Hi Karen. Try thinking about it this way instead: "What makes things fall to Earth? I think that what it is, is that you've grown up at the bottom of a gravity well i.e. on a planet, so it seems natural for things to fall, but really the nature of things is to stay where they are, or if moving, to keep moving at a constant rate.
Space is doing that. Sorry, I put my blog address again: http://ian-titen.blogspot.com/2009/07/view-from-event-horizon.html
Welcome and
Thanks for your posts .. let me read them some more and think them over a day or so before I reply. Takes me a bit for it to sink in!
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I like to look at it in terms of Energy.
If the Earth started a very long way away from the Sun ('infinity') and fell in towards it on a direct path, it would gain a certain amount of Kinetic energy (i.e. be going at a certain speed) by the time it arrived at our present distance due to it accelerating all the time it was approaching the Sun. That amount of energy is called its Gravitational Potential Energy - it is the work which is available from bringing the Earth from infinity to its orbital position. (It isn't 'quite' at the bottom of gravity well - it's 150 million km away from it)
If you could then make it 'turn sharp left', so its motion was tangential, it would go into a circular orbit- attracted to the centre but going just fast enough not to fall or to escape. Its Kinetic Energy would be exactly the same as its GPE. That's the situation for every orbit. The potential energy would be the same amount (but negative, because we got work out of the process of falling) as the KE. Its total energy would be zero.
If it didn't quite turn hard left - went off at a different angle - then its orbit would be an ellipse (which, of course, it is). The total amount of energy would still always be zero but when it was further away it would be going slower (less KE) and its PE would be less negative - still adding up to zero and vice versa when it was closer.
Rambling and confusing but interesting - total energy = zero!!
Thank you Sophie!! will reread this one also.. sorry it takes me a few times through to make it stick and allow my brain to get it!