(c) What are the two important properties of lubricants? Discuss briefly the effect of temperature and pressure on them. (d) Calculate the viscosity index of an oil whose viscosity at ambient temperature (40C) is 0.001 kg/m knowing that that oils with viscosity index of zero and 100 has viscosity of 0.006 kg/m s and 0.004 kg/m s respectively at 40C. (e) State Petroff's equation for a concentric (lightly londad)