gravity nut重心铊gravityn.重力；庄重；严重；严肃gravity to fall不限比重gravity closing自重闭合gravity packing重力填充法gravity rollers滑动滚柱gravity culvert重力排水涵洞gravity changes重力变化gravity incline轮子坡,重力坡gravity crusher重力破碎机gravity-meter比重计； 重力计gravity dumping重力卸料