What makes a planet spin?
538810
The effect known as the Gyrous of Rotation causes planets to spin. When the planet is born and begins to condense out of its accretion disc it contracts and this puts a turning moment about the planets common centre, similar to a ballet dancer pulling in their arms in order to spin faster. JULES
35969
The Earth rotates (spins around).  Sometimes a side is facing the Sun and is in daytime.  Sometimes it is not and is in nighttime.
481150
the earth spins at 1500 mph.  If you take a ball and spin it extreemly fast you will find that the center of the ball will grow and the poles will flatten.  It is like driving a car very fast.  The higher up ion speed you go the lower to the ground it will become.  I has to do with Volocity.
736348
The Earth's rotation began as the matter, that came together to produce our planet, gradually increased and compressed upon itself.\n\nHave you ever seen a figure skater when they go into a spin?  Notice they spin faster when they pull in their arms and legs.\n\nSame effect.\n\nGravity is actually a property of mass.  \n\nGreater mass = Stronger gravity
145598
The Earth was formed spinning (like a top) and it just hasn't stopped spinning since then.  There is very little friction that would slow it down (space is pretty empty).\n\nThere are different theories as to why it was created spinning.  But most likely it formed from gas and dust that was swirling, and that angular momentum is still with us today.
1090455
They start out as an enormous gas cloud. Gravity causes the parcicles in the cloud to spin around the point of center mass, and the velocity of the spin subsequently flattens it into a disk. That's how galaxies, and on a much smaller scale, planetary systems form.
661102
It ORBITS round the sun because of the suns gravity. It also SPINS on its axis, similar to earth but much faster. (takes half the time of earth to spin and it is much bigger)
707945
Earth's graceful 24-hour rotation rate is one of the traits that makes our planet so friendly to life, allowing most parts of Earth to stay a nice, comfortable temperature as they are bathed in sunlight during the day and darkness at night. \nEach planet in the solar system has its own unique rotation rate. Tiny Mercury, sizzling closest to the Sun, takes 59 Earth days to turn around just once. Venus, the second planet, rotates once every 243 Earth days. What's more, Venus rotates backwards from the direction of its orbit around the Sun, as do Uranus and tiny Pluto. Uranus even lies down on the job, rolling around with its axis of rotation pointed nearly toward the Sun.\n\nWhy do Earth and the other planets rotate at all? It will help to understand how our solar system formed. Almost five billion years ago, our solar system had its beginnings as a vast cloud of dust and gas. The cloud began to collapse, flattening into a giant disk that rotated faster and faster, just as an ice skater spins faster as she brings her arms in. The Sun formed at the center, and the swirling gas and dust in the rest of the spinning disk clumped together to produce the planets, moons, asteroids, and comets. The reason so many objects orbit the Sun in nearly the same plane (called the ecliptic) and in the same direction is that they all formed from this same disk.\n\nYou can visit this nasa site which has audeo narration and animation on earth rotation.\nhttp://spaceplace.nasa.gov/en/kids/phonedrmarc/2003_march.shtml
880350
It rotates and revolves, just like the planets. It rotates in the same direction as the earth (counter-clockwise), and completes a rotation about once a month. (Because the sun is gaseous, its equator and poles rotate at different speeds.) Galileo discovered that the sun rotates from watching the movement of sunspots. Meanwhile, the sun revolves around the center of the galaxy, in much the same way that the earth revolves around the sun.
126034
The planets revolve due to the conservation of angular momentum.  When the dust in space collapsed under the weight of its own gravity, it was not moving symmetrically about the center of gravity (located where the sun is).  So when it formed the planets, the sum of all angular momentum of the planetary material about that center of gravity was conserved (due to the conservation of momentum--see Newton for details).  Hence, they revolve.\n\nGravity keeps them from flying off into space, and angular momentum keeps them from falling into the sun.  When these forces balance eachother, you get on body orbiting another (although technicall, both bodies orbit the center of mass, which is only slightly displaced from the center of the sun due to the tremendous mass of the sun).
1157171
As Debster92 pointed out, there is no way to stop the Earth from spinning once it starts.\n\nAlso, and perhaps more importantly, there is absolutely no way to get it started again if it did stop.\n\nThe angular momentum imparted on the solar system as it coalesced out the primordial gas cloud is what causes all the planets to spin and rotate as they do today.  If one were to somehow stop a body from rotating, it would take tremendous energy to get it started again.
457404
All the planets in our solar system rotate in the same direction with the exception of Venus which rotates *very* slowly in the opposite direction.  It was theorised that it once suffered a glancing blow from a very large object that reversed its spin.\n\nHmm - by rotate I mean on their own axis - not around the sun, in which case all planets go the same direction.
505384
We can see the sun rise and set, and it would be impossible for the sun to revolve around the earth because of the huge difference in math, so the only explanation is that the earth is spinning.\n\nIn reply to the first two replys, the sun is not the center of the universe, it is the center of the solar system. Also, because of the sun's gravity, we REVOLVE, but that has nothing to do with rotation. MOMENTUM is what causes us to not feel the spin/movement, not inertia.
862988
Earth and the other planets were formed from a giant cloud of gas and dust revolving around the primitive sun. As in any other moving fluid, local whirlpools kept appearing and disappearing all the time. \nAs the cloud started to cool, local perturbations caused density variations : some whirlpools got lumpier than others, just as in a bowl of porridge when it cools off. They thus grew more stable and accumulated more matter because of their increasing gravity. On further cooling, these separated out as planets, molten globes of matter still spinning furiously.\nEven when the planets solidified at last, they retained a part of their original spin. That's why the Earth and the other planets are still spinning around their axes. That's what, thankfully for us, creates days and nights.
70654
Here is an answer i found in physlink.com\n\n"Stars and Planets form as a result of the gravitational collapse of accreting material. Any net translational motion of that initial material is accelerated as its radius of rotation decreases. This is due to the same conservation of angular momentum principle that makes skaters and divers spin more rapidly when they bring their arms closer to their bodies. In its extreme, this effect can make collapsed neutron starts spin many times each second, creating the regular beat of pulsars as observed from Earth.\n\nOnce an initial spin was established for the Earth, the same conservation principle says that its angular momentum will continue unless it can be transferred to another object. With no significant frictional forces to allow that to happen, the Earth can continue to spin indefinitely without any further prodding."\n\nCourtesy:- http://www.physlink.com/Education/askexperts/ae201.cfm\n\n\nBy the way...The speed of rotational (of Earth) at the equator is about 1,000 miles per hour.
467215
Spin relative to what?\n\nThe spin of the Earth about its own axis causes day and night but only because the spin is not synchronised with the orbit of the axis around the sun.  Mercury spins once on its axis for every orbit and so always has the same face to the sun.  It could be said in this case that Mercury does not spin, but that is only relative to the orbit of Mercury.\n\nImagine a frame of reference that is fixed in space like the grid lines on a map.  If a planet did not spin on its axis relative to this reference, then it would have a day/night cycle that took one orbit to complete (this would be one year for the Earth).\n\nIt is also believed that the spin of the Earth contributes to the generation of the magnetic field, so if the spinning stopped or slowed (relative to any reference) we could loose the magnetic field and thus be exposed to higher radiation levels from the sun.
388209
For years it was thought that in the case of Venus that the Earth was the culprit. It is a curious fact that as Venus rotates three times on its axis in 729.27 days, the Earth goes twice around the Sun ( 728.50 days) This has suggested to many dynamicists that Earth and Venus are locked into a 3:2 tidal resonance. There are many bodies in the solar system that seem to be locked into various kinds of spin-orbit resonances, especially families of asteroids with the planet Jupiter. Mercury also seems to be gravitationally locked into some kind of resonance with the Sun since its day (58.646 days) and its year ( 87.969 days) are also in the proportion of 3:2. \n\nwhat happened in essence is that venus spins once a year which is about zero rotation in the normal planetary sense.  evidently the way the solar system formed it just sucked the spin out of venus.  that probably accounts for why it's a greenhouse.