The electrostatic energy between a dielectric scanning force microscope (SFM) tip and a point charge is obtained in closed form as a function of the separation of the two objects. Applications of this result to both spherical and arbitrary tip shapes are discussed. Also, utilizing kinematic data, a method is given to experimentally extract the force due to the tip-sample interaction from a typical SFM instrument. This is done by analyzing the time dependent motion of the tip. The result is based on the use of a time dependent analysis of the force distance curve which is unavoidable in motion regimes in which the tip accelerates, as in the snap-to-contact process.