text: if the individual links of the track of a "bulldoser" --- while they are on the ground? do not move, does this mean that the links on top of the chain are moving twice as fast as the machine moves? you are correct.  the tracks are powered by cogged wheels driven by the engine and work like the wheels of a car except they run along the track instead of the road bed.  look at the wheel when it is moving.  the bottom point is momentarily fixed to the ground and the top point is moving straight ahead with a momentary velocity.  the axel which is half way between the top and bottom is traveling at the average velocity:  velocity (axel) = (vtop + vbottom)/ 2 = (vtop + 0)/2 = 1/2 vtop  the machine moves at the speed of the axel; proving your point.  an even better illusion is the fact that when a locomotive speeds down a track, part of it is always moving backwards (hint: the part of the wheel flanges below the top surface of the track!).