Too much heat causes the cell to turn down.
gravitational force
The force of the convection cell is bumping into the lithosphere which cause's it to turn at point a
The force that causes a convection cell to turn is the Coriolis force, which is a result of the rotation of the Earth. This force deflects moving air or water in the cell, leading to the rotation that defines a convection cell.
Forces such as gravity, friction, tension, and applied forces can cause acceleration in an object. When an unbalanced force acts on an object, it can cause the object to accelerate in the direction of the force.
The convection forces of plate tectonics.
thermal convection is the primary force that cause the sea floor to spread
unbalanced force
An unbalanced force will cause acceleration in the direction of the force.
The force required to cause the yielding of the solidis called the yield force.
Any force will do, as long as it's an unbalanced force (the sum of all forces acting on the object must not be zero).
Convection currents in the earth's mantle cause the plates to move. When this happens, mountains can form.
the movement of convection currents in the mantle is the cause of plate motion.