The Law of Universal Gravitation


The force of attraction F between two objects with respective masses m1 and m2 separated by a center-to-center distance R, anywhere in the universe, is described by Newton's Law of Universal Gravitation:

The two postulates of this law are:

  • The force of attraction is directly proportional to the product of the objects' masses

  • The force of attraction is inversely proportional to the distance (taken from their respective centers) squared

If we combine the above statements mathematically, we obtain the following relation:


noteThis relationship is known as an inverse-square law.  This means that one factor (F) is inversely proportional to another factor (R) squared

 We translate the above relationship into a definite equation by removing the "proportionalty symbol" (proportionality sumbol) and replacing it with the "equal sign" (=) and a constant.  The symbol for this constant is "G"


Gravit1 (1)



  • F is the force of attraction between two masses m1 and m2 anywhere in the Universe, and
  • and, G is the Universal Gravitational Constant: G = 6.67 X 10-11 Nm2 /Kg2

noteThe animation below is a very simple illustration of  the inverse-law law 



 noteNotes: When you use the above equation 

  • Observe proper units (mass in kg, distance in m, Force in [N]
  • The distance R  has to be center-to center; i.e. from the center of one mass to the center of the other
  • Don't forget to square the distance R
  • Remember the significance of the Inverse Square Law