Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 13/10/2007 18:28:31
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Dear Spinning Top Experts,
As I understand it, the Earth is spinning a little slower each day.
Does the same apply to it's orbit around the Sun. Is the Sun gradually spinning slower too?...what about all the planets ?..and their orbits ?..black holes ?.....what about the spin of the galaxy ?....is everything slowing down ?
ewe spin me right round baby right round !! [:)]
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The Earth is slowing donw largely because of tidal interaction with thte moon. Tidal interaction with the sun wqould also tend to slow it down, moving towards a tidal lock, or a small ratio resonance. That will be accompanied by an increase in the radius of its orbit.
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Everything tends to lose energy because of frictional effects although these may be very small in the case of planets rotating and obiting however the effects can be different. rotating things subject to tidal drag usually slow down unless they are rotating slower than the orbital period orbiting body that is causing the tidal drag in which case the tidal drag would speed up the rotation. Thats why the moon is locked with one face towards us. for the eart orbiting the sun (or a satellite orbiting the earth) losing energy by for example atmospheric drag results in the orbital velocity increasing. This is a bit counterintuitive but true
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two questions
why does atmospheric drag cause a planets orbital velocity to increase?
And are we actually measuring planets rotation slowing, or is it just a prediction?
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Actually the moon was once spinning faster and was slowd down so that it now only presents the same face toward the earth. There are other moons in our solar system that are in the same situation in reference to the planets they orbit.
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I think neilip, you will often read, the earth is slowing down due to friction, all the planets used to rotate faster blah blah blah, but those statements are not correct.
In fact the earth is speeding up! for example a leap second occurs every 500 days or so, but since the earth is speeding up they had to delay it recently. This speeding up has no explanation that im aware of, and has modern day scientists a little confused.
Another example is jupiter, jupiter rotates the fastest of all planets, it also has the greatest atmospheric drag of all planets, scientist have hypothesized that it should slow the fastest of all, but no slowing affects have been observed.
So if you hear somebody somewhere say everything is slowing down, ask them what they are basing that on. Chances are the answer will be, well it would have to be slowing down, right?
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To understand why earth satellites (and probably planets) speed up as they lose energy before burning up in the atmosphere you have to think of the situation in terms of energy. The attractive force of gravity is like a hole that you fall down so the deeper you are in the gravity pit your negative energy compared with being a long way away from the pit is greater so as the potentisl energy decreases by the conservation of energy your kinetic energy (ie velocity) must increase. Another way of looking at it is that as planes dive they speed up even though the wind resistance gets greater.
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okay i see what your saying now, i thought you meant that atmospheric drag makes planets rotate faster directly, not indirectly.
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One would expect that as the Earth warms up due to more CO2 the oceans will expand hence the rotation will slow done a Little.
This will be due partly to the melting of the ice caps and partly due to thermal expantion
See http://environment.newscientist.com/article/mg19626264.700-how-el-niño-slows-the-earths-spin.html