Also why doesn’t sun attract the planets, at least the inner ones like Mercury inside it that is,what keeps Mercury from clashing with sun?
What makes the planets to rotate around themselves while revolving around the sun?
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Printed from: http://arezeez.com/2009/11/29/what-makes-the-planets-to-rotate-around-themselves-while-revolving-around-the-sun/ .
© 2010.
© 2010.
The important concept to remember here is angular momentum which is conserved!
The sun was formed from a rotating cloud of gas and dust (proto-solar system). When the center of this cloud was big enough and the pressure high enough to start fusion, the star "turns on" creating the sun and thus the solar system. Everything else revolving around it maintains the same rotation if the geometry of the body is unchanged.
If a planet had the ability of getting bigger or smaller (which could technically be possible with gas giants like Jupiter and Saturn, but we will never see such a scenario), the bigger the planet gets the slower would rotate and vice versa… angular momentum is conserved!
Other things that would affect a rotation of a planet are tidal forces and collisions with other bodies which will transfer momentum.
Mercury falls toward the sun all the time. But its speed in a straight line at right angles to that fall carries it far enough forward also. That distance forward and down together make a curve that is the same curve of the sun’s surface (approximately). There is a serious variation in the speeds and distance from the sun because Mercury orbits in an ellipse, not a circle. But it makes no difference. Mercury gets no closer to the sun, inspite of constantly being dragged toward it by gravity.
This idea was put forth by Newton hundreds of years ago. If you had a very tall mountain on Earth, and a powerful cannon on top, a gunner could fire horizontally. The cannon ball would not hit the earth. As it fell by gravity, it goes forward too, and the curve resulting is the same curve of the earth’s surface. So it never gets closer. And about an hour or so later, the gunner who fired the cannon has to duck as the cannon ball comes at him from the other direction.
Purists who say that the real story is given by Einstein. He said the mass of the sun makes space-time in its region curved, not straight. As Mercury seems to go in a straight path, this curved space makes it go around the sun. Not nearer, not farther, but always orbiting at the same distance.
As to why planets rotate about an axis, that happened to begin long ago. We think in the case of the Earth, a sideways hit by a very large object (size of Mars?) made it spin the way it does now. As to the other planets, perhaps a similar process when they just started to form caused the spin. It may have been slow at first. Mercury and Venus spin very slowly. Jupiter and other large planets spin fast. Perhaps, as those large planets contracted from even larger gas and dust clouds, they speeded up in spin. The law of conservation of angular momentum supports that idea.
Because of inertia, the planets close to the sun don’t clash into the sun. Inertia causes a counter to gravity and it causes the planets to revolve around the sun, not go in a straight line away from the sun and it doesn’t crash into the sun.
There is no force that causes the planets to rotate. Most of the rotation comes about from the conservation of angular momentum. Planets form out of a protostellar disk, which itself forms only because of the initial angular momentum of the cloud. The dynamics of a rotating body is of course controlled by forces like gravity.
Planets move around the sun and have intertia, so they have a resistance to fall into the sun.
in addition to falling toward the Sun, the planets are moving sideways. This is the same as if you have a weight on the end of a string. If you swing it around, you are constantly pulling it toward your hand, just as the gravity of the Sun pulls the planet in, but the motion sideways keeps the ball swinging around. Without that sideways motion, it would fall to the center; and without the pull toward the center, it would go flying off in a straight line, which is, of course, exactly what happens if you let go of the string.
Centripetal force prevents them from colliding with the sun while centrifugal force keeps them in their orbits.
The rotation is due to the conservation of angular momentum. It demands that a spinning body keep spinning until an external torque acts on it to change its state.
The planets started spinning due to some initial force and will continue to do so.