[neilep (OP)]

Why does the Earth Spin ?

Why do all the planets spin ?

Do you think spinning is prerequisite for planets in orbit around a sun ?

What determines the rate of spin ?

Men are the same as women, just inside out !

[Hadrian]

It spins because of the way it was made. Our solar system formed out huge cloud of gas and dust that started to collapse under its own gravity. As it did it started to spin. Pits of it gathered into swirling swirls that eventually formed into planets. As they did they kept their spinning motion. This is what happens when skaters pull in their arms and spin faster. As material groups together more closely and forms into a planet, it spins faster. The Earth keeps on spinning because there are no forces acting to stop it.





What you do speaks so loudly that I cannot hear what you say.

[JimBob]

Hadrian,
Almost no ...  There is one force slowing the earth down measurably - the moon's gravity. The effects of the planets and the sun are negligable compared to the moon's but do influence the earth, both increasing and decreasing spin, depending on their relative relationship to earth.



The mind is like a parachute. It works best when open.  -- A. Einstein

[neilep (OP)]

[?] What about the oceans ?..do they have a friction effect [?]

Men are the same as women, just inside out !

[ukmicky]

I thought the energy for the motion of the solar system came from the sun when it first ignited and when the blast of energy heated up the almost motionless surrounding cloud of dust and gas which then caused everything within to move about and gain angular momentum (spin) with help from the suns gravity



Michael

[another_someone]

quote:Originally posted by ukmicky
I thought the energy for the motion of the solar system came from the sun when it first ignited and when the blast of energy heated up the almost motionless surrounding cloud of dust and gas which then caused everything within to move about and gain angular momentum (spin) with help from the suns gravity

I would believe this not to be the case.

The actual ignition process would not generate rotational forces; and these would probably already have been in place in the gas cloud that existed from which the solar system was formed (or, at least, the localised region in which the solar system formed).

I would see it more as a manifestation if a weather system within the cloud, that would have has local rotational forces not unlike one has cyclones and anti-cyclones within the terrestrial weather system.  One of these cyclones, or anti-cyclones, then collapsed by a combination of its own gravity and a shock wave from a nearby super-none, and this collapse created the solar system, but maintained the rotational energy of the local cyclone/anti-cyclone from which it formed.

George

[Soul Surfer]

Angular momentum or spinning is just about the most fundamental thing about our universe.  It is at least as important as gravity.  In any isolated object or system angular momentum like energy is strictly conserved and the ignition of the sun could not affect it. it was a property of the piece of cloud that contracted to form the sun.  As a cloud contracts any tendancy to rotate becomes faster.  It is the same effect that causes the water to swirl as it goes down the plughole.

It is important to realise that most of the angular momentum in the solar system is concentrated in the planets and NOT the sun.  the formation of planets is a way of getting rid of excess angular momentum that would prevent the cloud from collapsing to form a star.

Learn, create, test and tell
evolution rules in all things
God says so!

[neilep (OP)]

Well, I'd just like to thank you all for your kind responses.

So it seems that spinning is indeed prerequisite as a consequence of the planets formation..

If I may ask a couple more question please :

Presumably this is why the planets (for the most part) spin in the same direction [?]..I gather there is one exception but that may be down to a collision. Sorry, can't remember which planet it is.

.......and lastly....would there be any difference at all to life on Earth, the formation of the Earth, if the planet span the other way [?] same speed, just the rotating the other way [?]

Thanks all...Happy Bank Holiday.

Men are the same as women, just inside out !