Why do planets rotate about thier axes, and why do they revolove around the sun?

Question

Centripetal force, centrifugal force, all right, but how is such a delicate balance maintained in nature? Why don't planets collide with each other and stuff like that?

Answer 1

It's thought that the planets & sun condensed from an original, huge cloud of gas and dust that was swirling around in more or less random directions. Now, if the cloud were perfectly stationary instead of churning & swirling, then all of its particle would soon dive straight towards the clould's center of gravity (due to gravitational attraction), and would collapse into one big, non-rotating mass that would become a star.

But the fact is, the cloud DOES churn and swirl, and if you add up all the angular momentum in all the random churning and swirling parts, the total sum will never be exactly zero (as an analogy, if you choose a million random positive and negative numbers, their sum will hardly ever be exactly zero).

And this means the cloud has a net angular momentum--a very slight overall "spin".

As the clould condenses, the spinning becomes more rapid due to the conservation of angular momentum (just the way a skater spins faster when she pulls her arms in to her sides). At the same time, this tends to make the clould flatten into a disk, and the spin becomes more noticeable. Clumps of matter within the cloud-disk begin to collapse into planets which have the same spin orientation as the overall clould. so what you finally end up with is a collection of objects which each have a bit of the original cloud's original angular momentum.

> Why don't planets collide with each other and stuff like that?

Computer models and hard evidence show that there were LOTS of collisions in the early days. There were trillions of small objects rather than just a handful of large objects like we have today; and their paths crossed quite frequently. But eventually such collisions stop (or become very, very rare), and the system "settles down" into a fairly stable state. The reason is simple when you think about it. If huge rocks are whizzing about every which way, they're going to collide; and the collisions are going to cause their paths to change randomly. But if the huge rocks are going around the sun in nice circles, then each of them stays in its own "lane," and they don't collide--hence they no longer change their paths. So, after many random collisions, things eventually settle into paths which no longer cross; that is, into circles or near-circles.

Answer 2

Our solar system was once just a giant disk of loosely packed matter, and over time...matter began to clump together in dense clumps. The larger these clumps grew, the greater their overall gravitational fields became... pulling more matter into the pockets. It just so happened that the matter was originally spread far enough apart, that the outlining matter created their own gravitational fields that counteracted the strong pull of the field in the centre (our sun). Eventually the planets created a balance with the sun, based on their size, distance from the centre, and rotational velocity. In essence, the planets and the sun were all create from the same source... unlike external celestial bodies such as asteroids and comets, which as we know have a very different path.

Answer 3

Sometimes things do collide with each other. Planets are not on perfect orbits, the earth is moving closer to the sun slowly every year.

Most scientists think that the moon was formed by a massive collision of some object into earth. The solar system has had time to calm down from it's initial, more chaotic, phase.

Answer 4

Why does every thing in space rotate???? The planets don't collide as all is in the balancing of the forces. They don't collide because they have been in their orbit for millions of years and they are so far apart. . Nothing will change unless it is acted on by other forces.

Answer 5

The rotation of the planets around their axes relates to the origin of the solar sytem itself.It is believed that the sun and its planets have formed from a primordial revolving disk of hot gases known as the solar nebula, the sun having formed in the centre of the disk.Even though there are several theories about the origin of the solar system,none is universally accepted.However there are some well defined conformities(similarities) in the solar system which can to some extent help us to know about the origin.They are as follows:
(1)The sun rotates in its axis from west to east as viewed from the north celestial pole in space.
(2)Planets also orbit the sun from west to east almost in the same plane and direction as the sun rotates.
(3)Most of the planets rotate on their axes from west to east nearly in the same plane with slight deviations.
(4) Planetary orbits lie at regular intervals from the sun,i.e.,roughly twice the distance from the sun as its next inward neighbour.
(5) Satellites of planets tend to orbit in the same plane and direction of the rotation of the respective planets,with a few exceptions.
According to the theory of conservation of angular momentum, the revolution and rotation must have originated at the time they solidified(formed) from a rotating gaseous nebula.The above mentioned conformities indicate that the sun and its planets must have formed from the same rotating disc as their rotation and revolutions are in the same plane and in the same directions.
Probably,the rotation in the same sense as the revolution must have been the natural dynamical motion with least resistance.Subsequent changes in the case of a few planets(for example venus rotates backwards and the axis of some planets have a tilt of the axis in different directions) must have been brought out by gravitational tidal effects and planetary perturbations.

Answer 6

Newtons laws of motion.


AJ you were doing real well until the last line. Comets and asteroids are a permanent part of our solar system. Comets fall in from the Oort cloud when their orbits are perturbed.
Asteroids come from the belt between Mars and Jupiter and they go into elliptical orbits for the same reason.
The reason that they do it and planets don't is planets are so, so so much massive.

Answer 7

gravity