Final answer:
The driving force behind plate movement is convection in the mantle, where hotter material rises and cooler material sinks.
Step-by-step explanation:
The driving force behind plate movement is the process of convection that occurs in the mantle. The mantle is the layer of hot, semi-fluid rock beneath Earth's crust. This convection is driven by the transfer of heat from the interior of the Earth to the cooler regions near the surface. The hotter material in the mantle rises, while the cooler material sinks, causing the movement of tectonic plates.