What Causes The Earth's Plates To Move?

The gravitational pull from the sun and other planets.
thanked the writer.
Because of the Earth rotation and revolution
thanked the writer.
The reason that earth's plates are moving is because that the mantle is shifting around causing the plates to move.
thanked the writer.
The direction of the movement of one plate in relation to another depends on geometric principles that govern the behavior of rigid bodies. Earth's plates behave as rigid bodies. That is, the distances between three points on the same plate; it just like New York, Miami, and Bermuda on the North American Plate do not change, no matter how the plate moves. But the distance between, say, New York and Lisbon increases because the two cities are on different plates that are being separated along a narrow zone if spreading on the Mid Atlantic Ridge. Two primary geometric principles govern the sliding of plates on our planet, earth.

I. Transform boundaries reveal the direction of plate movement
ii. Isochrones reveal the positions of plates in earlier times.

According to first principle, no overlap, buckling or separation occurs along typical transform boundaries. The two plates merely slide past each other without creating or destroying plate material. Look for a transform boundary if you want to deduce the direction of plate motions, because the orientation of the fault is the direction in which one plate slides with respect to the other. While isochrones on the seafloor are roughly parallel and are symmetric with respect to the ridge axis along which they were created.
thanked the writer.