一圓柱形機軸在固定的軸承中勻速轉動。軸徑d=20cm,軸承寬b=20cm,潤滑油粘度μ=0.2Pa·s,軸承轉速為n=150r/min。設間隙分別為δ=0.8mm,0.08mm,0.008mm時,求所需轉動功率。