Figure 7-2 Solid Rotation Versus Differential Rotation (a) All parts of a solid object rotate together, but (b) a rotating fluid displays differential rotation. To see this, put some grains of sand, bread crumbs, or other small particles in a pot of water. Stir the water with a spoon to start it rotating, and then take out the spoon. The particles near the center of the pot take less time to make a complete rotation than do those away from the center.