text: this question take us to the cause of gravitational force, acco0rding to Einstein the time-space cojunction is bended nearby mases, and of course it is bended more near the higher mases. so when ane body fall in the time-space bendind for another mass it will be forced to take certain tracks by time-space bending so it begin to rotate in an ecliptical tracks arround the other body (like earth orbiting the sun). the principle of equivalence says that also light is forced to take certain tracks too near by masses for the same reason, this principle was proofed in 1919 during a famous solar eclipse, they observed some stars in the day near the eclipted sun and found that its position was little shifted (indeed the comming light from these stars curved by the mass of the sun) and this causes a famous astronommical phenomena called Gravitational Lenses which you can find some photos and comments about it in Internet.\ni hope that i could give you the benefit, Regards.