why is oil or grease applied to the moving parts of the machine? Share with your friends Share 8 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. 11