Monday, February 1, 2010

Why does the moon keep its orbit around the earth?

The moon...
The only natural satellite of the earth has always attracted the minds and thoughts of humans. Starting the Egyptians humans tried to explain why the moon circles around the earth. Galileo studied the moon with its telescope wich helped im develop his theories but even he did not explain why the moon circles around the earth. But when Isaac Newton sat in the garden of his fathers farm and an apple dropped on his head he suddenly found the answer. (Of course this is just a legend!) Up to this point everyone knew that the earth attracted objects.(gravitation) Also widely known was that the earth circles around the sun. But only these two attractions could not explain the monthly circle of the moon around the earth. Isaac Newton finally developped the theory that the moon has to attract the earth too.He had the magnificent idea that every particle of mass attracts each other. This can be related to his third law. (Actio/Reactio) The gravitational force of the earth attracts the moon. In reaction, the moon attracts the earth with gravitational force.  This idea was the start of a project that a few years later resolved in a formula for universal gravitation between two objects. FG=(Gm1m2)/r^2 If we plug in the mass of the earth and the moon and add the radius between them, the resulting force of gravitation bewtween the moon and the earth explains the movement of the moon. Relating this to Newtons second law (F=ma) and the fact that the gravitational force of the earth is the only relevant force acting on the moon, the moon circles around the earth with a centripetal acceleration described by ac=v^2/r, where ac=Fg/m(m), because of (EF=FG=mac). Further Newtons idea helped develop the formula for the gravitation on the  moon surface:  g=GM/r^2 In both formulas concerning universal gravitation, there appears a big G. This is the gravitational constant that represents 6.67*10^-11 Nm^2/kg^2.

Newton may have only developed the idea and laws that helped solve this problem but in Physics, HE is the man who conquered the moon....


  1. Your project should have a question that has to be answered using physics principles.
    What exactly is your question?
    Are you trying to explain the period of the moon?
    The forces that keep the moon in orbit?
    Also, how can you justify the equation for centripetal acceleration using the attraction between moon and earth and moon and sun?
    Your project needs significant work!

  2. Ok, I rewrote it and tried to answer the question directly. I hope that this will answer the the question for a question as much as the question it self. I will add an example calculations this evening. . .

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