Hi, i surely do appreciate some help here.. How is gravity on the earth surface related to the circular motion of the earth about its axis? If i'm not wrong, my lecturer once taught me that i can actually equate both gravitational force and centripetal force together since they are both the same. (Gravitational force holds all objects on earth together and move them in a circular orbit which is also what centripetal force does on the objects moving in circular motion.) which i think by further simplifying the equation GM/r^2 = rw^2 gives kepler's law, T^2 is directly proportionate to r^3. Alright, now here's the problem. If both GM/r^2 and rw^2 can be equated like what my lecturer said, then both of the equation should give the value of gravitational field strength of the Earth on its surface which is (9.81ms^-2) However, by workin out rw^2, i'm unable to get the value 9.81ms^-2, what i get was only 0.03ms^-2. Is there a problem with my calculations or had i miss out certain things. I'm really quite confused over this. Any help given will be greatly appreciated. Thanks!