Centripetal acceleration question?

Discussion in 'Physics & Math' started by theorist-constant12345, Jan 27, 2015.

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  1. theorist-constant12345 Banned Banned

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    The Earth orbits the Sun by centripetal acceleration.

    Is there any possibility that the force of orbital rotation is created by the Earth only ever having one side in the Light and in applying Newtons Laws of motion, the EM radiation applies a force perpendicular to the Earth that pushes the Earth around whilst being held by gravity?


    The Crookes device shows the force is directional to the light, the rear of the devices ''propellers'' are black.
     
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  3. OnlyMe Valued Senior Member

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    The earth's orbit is the product of the earth's inertia associated with its linear velocity and the cenripedal force associated with the gravitation between the earth and the sun.

    No. There is not enough momentum associated with the light from the sun.., and it would contribute to centrifugal force rather than any centripetal force.

    What is happening with a radiometer is very different than what is happening with orbits. You should just look up explanations describing how and why radiometers work, should be easy to find on the web.
     
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  5. theorist-constant12345 Banned Banned

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    Thank you for your answer and I have a few questions about your answer if you do not mind answering them please.

    ''No. There is not enough momentum associated with the light from the sun.., and it would contribute to centrifugal force rather than any centripetal force.''


    Yes the force contributed by the Sun would be of centrifugal force and the force of gravity would be centripetal. You say there is not enough momentum by the force of light, in the Crookes device the ''Paddles'' of the device are a small area, so how would the force of light effect a larger area?

    How much of a difference would the Crookes device have in speed if we removed the friction?

    The Earth is under no friction, the coupling of the earth to the Sun and torque could be explained by this process?

    I understand present version of orbital rotation please do not think I am trying to change that, I am just asking if this has any effect.
     
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  7. billvon Valued Senior Member

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    No.
    1) The force is very close to zero compared to the other forces on the Earth.
    2) The force is symmetric; it acts on the entire sunlit side, so would neither speed nor slow rotation.
    3) No external force is necessary to continue either rotation of the Earth nor its revolution around the Sun.
     
  8. billvon Valued Senior Member

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    It would not move at all. It requires gas inside the envelope to operate.
     
  9. theorist-constant12345 Banned Banned

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    You say the force is very close to zero , that means obviously that it is not zero. How much force is needed to move an object in space?
     
  10. theorist-constant12345 Banned Banned

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    Well that answers that then.
     
  11. billvon Valued Senior Member

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    Any force will move an object in space (F=MA.) Forces like:
    - Solar wind direct impact
    - Meteor impacts
    - Solar wind interaction with the magnetosphere
    - Re-entering spacecraft
    are negligible compared to the force that keeps the Earth in its orbit (the gravity of the Sun.)
     
  12. theorist-constant12345 Banned Banned

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    I think I understand what you are saying. Are you saying that the force of the light on the huge mass of the Earth will not be enough force to compensate for the suns gravity pull although very little force is needed to accelerate mass in space?

    Are you certain this is not where the kinetic energy comes from to retain the motion of orbit?
     
  13. exchemist Valued Senior Member

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    The kinetic energy in orbiting planets comes from the kinetic energy in the rotating cloud of gas and dust from which the sun and planets are thought to have originally condensed. In the absence of any forces slowing them down (and there are almost none in space), their motion would be expected to continue indefinitely. You do not need to keep giving them energy in order to "retain" them moving in orbit. You only need to do that if there is a source of drag of some kind.
     
  14. theorist-constant12345 Banned Banned

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    This is what is confusing me, you say there is no source of drag of any kind, yet the Earth and the Sun are being pulled together by gravity, is this not considered drag?

    I would assume this to be drag, gravity pulls back, so are you sure that in some way the force of light on the planets does not give a continued supply of KE?


    Is the Northern lights not a sign of friction?
     
  15. OnlyMe Valued Senior Member

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    It seems others have provided clarification, for most of your questions, so I will only correct an issue with the above sentence.

    Any momentum associated with light striking the earth would not be a centrifugal force. It would be, as others have mentioned an insignificant linear force, pushing the earth in the direction the photons are traveling. It is insignificant because the total momentum of all of the light from the sun that hits the earth, is insignificant when compared to the earth's inertial mass... The earth is a big rock and light represents a comparatively small linear force.

    Centrifugal force is a ficticiuos force, and in this instance, is the earth's inertial resistsance to a continous change in it linear velocity, which winds up an orbit around the sun. This must be thought of in the Newtonian context, where gravity pulls on the earth and the earth's own momentum is linear. Centrifugal force is an inertia resistance to any change in a massive object's linear velocity.
     
  16. OnlyMe Valued Senior Member

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    No! There are essentially two forces, again in a Newtonian sense, the earth trying to move in a straight line past the sun and the gravitational interaction between the earth and the sun, pulling the earth's path into an orbit around the sun.

    Gravity is not acting in the opposite direction, as the earth's linear velocity. The earth's inertial momentum and gravity act at close to right angles to eachother.

    Yes but again, compare the total momentum associated with that friction to the total inertial mass of the earth and it becomes insignificant....

    When you start to look at small things like how light affects the earth's orbit or the northern lights (which are caused by the solar wind not photons), you also have to start accounting for things like the affect of heat loss on the dark side of the earth. But all of these things are so small compared to the earth's inertial mass that they are and remain insignificant.

    Gravity is significant because it is proportional to the total mass of both the earth and the sun.
     
  17. theorist-constant12345 Banned Banned

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    I understand that ''centrifugal force'' is a fictional force, I understand that the force of light is perpendicular to the Earth. Einstein states that the linear velocity of the Earth trying to go in a straight line is equal to the perpendicular force of the gravity .

    The Suns light force is perpendicular to the Earth, so my question is , if gravity of the sun all of a sudden stopped, but the light continued with a force perpendicular to the Earth, would the Earth by the only force present be pushed away at a perpendicular velocity?
     
  18. theorist-constant12345 Banned Banned

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    if the force was perpendicular the Earth is trying to go in a straight line , a perpendicular one?
     
  19. exchemist Valued Senior Member

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    Yes. For a body in circular orbit, the force of gravity is always acting at right angles to the direction of motion. That's why it cannot slow it down or speed it up. All it can do is make it move in a circle, instead of the straight line path that it would follow if it were possible to "switch off" the gravity somehow.
     
  20. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    Stop making things up.

    No.
    Again.
    Any force from sunlight is negligible compared to the Earth's mass.
    As you have been told already.
     
  21. theorist-constant12345 Banned Banned

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    So the force of gravity to the force of the EM radiation and solar winds must be equal to orbit?

    There has to be an opposing and equal force?, the Sun not only pulls us towards it, it also pushes us out perpendicular , <a linearity outwards from the sun and not side ways>, to the force ?
     
  22. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    No.
    An orbit relies ONLY on the gravity acting on and speed of the body in question.
     
  23. OnlyMe Valued Senior Member

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    Notice earlier I kept saying, in a Newtionian sense. Spacetime, Einstein's baby, does not always fit well with your above statement.

    If there were no gravity, yes any momentum perpendicular to the earth's line of motion would change its direction.., but in the case of the light involved, it would be so small as to likely be unmeasurable over any meaningful time frame.
     
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