Q$4.($a$)$ Lubrication $($Boundary$,$ Transitional $\backslash$& Hydrodynamic$)$:

$($i$)$ Explain using diagrams the difference between Boundary, Transitional $($Mixed$)\backslash$& Hydrodynamic Lubrication in terms of the presence$/$absence of asperities in contact of the two surfaces, and their effect on the coefficient of friction.

$($ii$)$ Sketch a typical fully labelled $($schematic$)$ Stribeck Curve, showing the regions of Boundary, Transitional $\backslash$& Hydrodynamic Lubrication. $($General shape only is required$)$

$($iii$)$ Determine the Hersey Number, which is used to determine the co$-$efficient of friction between shaft and bearing separated by a lubricating fluid, if the fluid has a dynamic viscosity $(\backslash (\backslash$mu $\backslash ))$ of $0\mathrm{.}582$ Pas and an Average Load per projected area, $\backslash (\backslash$mathrm$\{$P$\}=500\backslash$mathrm$\{$~N$\}/\backslash$mathrm$\{$m$\}^\{2\}\backslash ).$ The shaft rotates at a speed $($ N $)$ of $1500$ RPM$.$