The optimum passage section figure of rectangle is square, and the rectangle has 4 optimum comer circular arcs which make the hydraulic loss of friction loss of per unit length passage the least.

The slightest motion of a patient in bed creates friction between skin and sheets and results in loss of cells from the skin's outermost layer.

With graphite particle content increasing from 5% to 20%, wear weight-loss and friction coefficient of the composites are obviously declined, greatly improving wear resistance of the composites.