Using a surface forces apparatus (SFA), we have studied the adhesion and friction of polystyrene (PS) films on mica having various molecular weights from 580 Da (T-g = -45 degrees C) to 1300 Da (T-g = +39 degrees C) at temperatures T from 23 to 65 degrees C, i.e., below and above T-g. The purpose of these studies was to establish how different static and dynamic properties and surface deformations, i.e., the contact and adhesion mechanics, of detaching and shearing polymer films change as one passes through the glass transition temperature, i.e., from solidlike or glassy to liquidlike behavior. At T > T-g the polymers behave like liquids, and at low detachment and shearing rates their adhesion and friction forces are accounted by their surface energy and bulk viscosity, although fingering instabilities and cavitation accompany the detachment. For the higher MW polymers (T close to T-g), the adhesion and friction forces increasingly depend on the density of chain ends at the surfaces. The adhesion hysteresis peaked close to the bulk T-g but also depended on the load, contact time, and detachment rate. Certain correlations and scaling relations were obtained. We discuss these findings in terms of the bulk and surface molecular properties of interacting polymer surfaces above and below T-g.