Final answer:
The motion of tectonic plates is driven by heat transfer within the Earth's mantle, where rising and cooling material creates convection currents that move the plates. These currents, along with other forces such as subduction and ridge push, are the mechanism behind plate tectonics.
Step-by-step explanation:
The force that makes the motion of tectonic plates possible is primarily due to the transfer of heat within the Earth's mantle, acting like a convection current. These currents are caused by the hot material at the deep mantle boundary rising upwards, then cooling and sinking again, driving the plates at the surface to move. This process is known as plate tectonics and it operates as a sort of conveyor belt mechanism, which is fundamental to many geological processes including earthquakes, volcanic activity, and the creation of mountain ranges.
Additionally, tectonic plates can move because of the forces acting at their boundaries, which include the force of gravity pulling down on heavier, denser oceanic plates as they subduct under continental plates, and ridge push, which comes from the upwelling of material at mid-ocean ridges. The motion of plates is complex and occurs on the spherical surface of the Earth, which means the speed and direction of their movement can vary based on their location relative to a rotation pole, often referred to as an Euler pole.