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Physics SL/HL: What is Newton's universal law of gravitation?

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The law is based on bodies of mass. It states:

  • The force of attraction between two forces is directly proportional to the product of the two masses.
  • The force is also inversely proportional to the square distance between them.

So:

gif.latex?F \propto M_1.M_2

gif.latex? F \propto\dfrac{1}{r^2}

Putting these two together gives:

gif.latex?F \propto \dfrac{M_1.M_2}{r^2}

In order to make them equal we need a constant (which is G. 6.674×10-11 N m2kg-2). The final equation results in:

gif.latex?F = G. \dfrac{M_1.M_2}{r^2}

Now, how is this linked to Coulomb's law? Well they're both extremely similar but for charges instead. However please remember that like charges repel and different charges attract. A common mistake is that they'll always attract just because that's what happens between two bodies of mass. So think of the force as the force the charges experience instead of the force of attraction.

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Now, how is this linked to Coulomb's law? Well they're both extremely similar but for charges instead. However please remember that like charges repel and different charges attract. A common mistake is that they'll always attract just because that's what happens between two bodies of mass. So think of the force as the force the charges experience instead of the force of attraction.

If I'm not mistaken, I think a better way of conceptualizing this is to see if the electrostatic force is positive or negative. Opposite charges attract; so if the force is negative, it is an attractive force. On the other hand, like charges repel, so if F is positive, it is a repulsive force.

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