why is oil or grease applied to the moving parts of the machine? Share with your friends Share 10 Ankur answered this Lubricants like oil, grease etc. fill up the irregularities of the surfaces, making them smoother. Hence, friction decreases. 3 View Full Answer Ash answered this Lubrication forms a layer between the two surfaces filling the spaces between the interlocks and making machine smoother to move. 12