The effect of increasing the temperature of a liquid is to reduce the cohesive forces while simultaneously increasing the rate of molecular interchange. The former effect tends to cause a decrease of shear stress, while the latter causes it to increase. The net results is that liquids show a reduction in viscosity with increasing temperature. Since with increasing temperature m increases in gases and decreases in liquids, the drag force will do the same. Consequently, the effect of increasing temperature will be to slow down the sphere in gases and to accelerate it in liquids.
Viscosity is a macroscopic transport property of a fluid.
Most microscopic theories of viscosity are phenomenological because it is very difficult to compute from first principles all the many particle molecular interactions that are responsible for the viscosity. Consider a liquid at say room temperature. It is these attractive forces that are responsible for the viscosity since it is difficult for individual molecules to move because they are tightly bound to their neighbors. As the temperature is increased the thermal or kinetic energy of each molecule is increased and the molecules become more mobile. The attractive binding energy is lessened and therefore the viscosity is reduced.