An equation relating liquid density and viscosity under transient pressure conditions is derived. The derivation combines approximate phenomenological descriptions of the viscoelastic compression of a liquid and the dependence of viscosity on pressure and density. Solutions of the equation for a “step”-pressure increase and a semielliptical pressure cycle show that density and viscosity of Newtonian lubricants may significantly lag pressure transients under concentrated-contact lubrication conditions. Qualitatively, the lag effects appear to account at least partially for anomalous experimental observations involving asperity interactions and elastohydrodynamic lubrication of rollers.

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