“Universal gravitation
What else can we understand when we understand gravity? Everyone knows the earth is round. Why is the earth round? That is easy ; it is due to gravitation. The earth can be understood to be round merely because everything attracts everything else and so it has attracted itself together as far as it can! If we go even further, the earth is not exactly a sphere because it is rotating and this brings in centrifugal effects which tend to oppose gravity near the equator. It turns out that the earth should be elliptical, and we even get the right shape forthe ellipse. We can thus deduce that the sun, the moon, and the earth should be (nearly) spheres just from the law of gravitation.”