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    Mass distribution and gravitational field

    The field outside a body with spherical mass distribution is well known but for a non simmetrical body (or a almost simmetrical body like the earth) which is the approach?. Do you know any reference? thank you
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    3.6 + 4.4 + 5.8 = 13.8

    just a simple question: having to round up the following numbers: 3.6 + 4.4 + 5.8 = 13.8 I could do this: 4.0 + 4.0 + 6.0 = 14.0 but wanting to keep the sum?
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    Cosmic rays

    most of the cosmic rays that hit the earth is made up of positively charged particles, like protons. This suggests that the earth has a growing excess of positive charge .... Is this true?
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    Magnetic forces

    May be a trivial question.... The forces that arise from the magnetic field are Lorentz forces that not make mechanical work. When a piece of iron is attracted by a magnet is accelerated and its kinetic energy increases: Who does the work necessary?
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    Action and reaction

    In a generic case of a mass point and an extended body to interact with gravitational force, the total force on the point admits a reaction to be construed as, on the extended body ? The total force on the extended body do not arise from the interaction between two points, but between a...
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    Gravitational force

    Hi, it is well know that the force on a mass point outside to an homogeneous sphere is as the whole sphere's mass is concentred on its centre. It seems that the reaction of this force (the total force of the point on the shepre) is applied on the centre of the sphere but, is it true? If this...