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Why do planets move?

  1. Apr 5, 2008 #1

    why electrons don't get stuck to the nucleus since they are attracted by it? what force stops them ?

    Why do planets move around the sun but never get close to it?

    Who gave them initial velocity so they can "fly" in an orbit around a bigger object like the sun.

    why are orbits not circular but eliptical :)))

    thanks for whoever is willing to answer my "maybe dumb questions"...:0

    thank u
  2. jcsd
  3. Apr 5, 2008 #2
    I think the answer to the second question would be centripetal force. They are orbiting fast enough to not fall into the little divot in space the star makes. Its like a marble in a funnel, but the marble is rolling fast enough to not fall in the middle.

    and the 3rd question: GRAVITY. Every object has it. The planet, starting out as bits of dust, was probably there for a long time, shortly after the star formed, then coalesced into planets, never ceasing to orbit its star that entire time.

    These answers are just what I, a "rookie" if you will, can come up with. Dont trust them 100%
    Last edited: Apr 5, 2008
  4. Apr 5, 2008 #3
    As the giant molecular cloud that was spawning our solar system was gravitationally collpasing (triggered perhaps by a nearby supernova), the consequences due to the law of conservation of angular momentum meant that this molecular cloud would spin faster and faster and flatten out. The bodies of our solar system formed from this collapsing, spinning cloud. That's where planets got the initial velocity to "fly" around.
    Last edited: Apr 5, 2008
  5. Apr 5, 2008 #4


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    Furthermore, in order for the solar system to NOT be spinning today, it would have had to condense from a molecular cloud that had zero net rotation - an incredibly unlikely event.
  6. Apr 5, 2008 #5
    Planets move around the sun and have intertia, so they have a resistance to fall into the sun. Like swinging a heavy object around in circles on an elastic band.

    Circular orbits are elliptical too except that the eccentricity of a circle is 0. Elliptical orbits comes from the fact that the planets angular momentum must be conserved and that the force changes inversly with the square distance from the sun. When the planet gets closer to the sun the force goes up, but so does the angular velocity so the planet gets sling shotted back out from the sun once it gets enough velocity, then slows down and then heads back towards the sun.

    Look up Kepler's laws of planetary motion.
  7. Apr 5, 2008 #6
    Electrons do not crash into the nucleus because both "orbits" and energy for electrons are quantized; they are discrete entities, not continuous. The "orbits" are discrete in that there are only a certain number of "allowed" orbits. They are like steps on a set of stairs...I guess you could say. An electron cannot just be in any old orbit, there are certain orbits for certain "places" around the nucleus called "shells", or "clouds." The discrete energy part is that energy is given off in packets called photons, and is not continuous. Therefore, when an electron is in a certain orbit, the atom is in a stationary state, and will not emit energy, so the electron will stay in its orbit. Say it does change orbits; it will emit the amount of energy equal to the difference in orbit energies in the form of a photon. This is in contradiction to electrodynamics, which says that an accelerating charge releases continuous amounts of energy. All in all, electrons can only be in discrete orbits and emit discrete amounts of energy, so there is much control held over there states.

    Please...nobody flame me for saying that this explanation says that the quantum world is determinate and non-chaotic, this is for the sake of conceptual understanding.
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