The friction behaviors of poly(tert-butyl acrylate) (PtBuA) thin films have been investigated at different temperatures (20-70 degreesC) and different scan rates (50 nm/s to 25 mum/s) by friction force microscopy. By variation of the external load, the friction responses at different depths of the film are also probed. On the basis of the shifting of data from different temperatures, a series of friction master curves (friction versus scan rate) can be constructed to span 7 orders of magnitude in scan rate. A friction peak, indicating the glass-to-rubber transition of the polymer film, is clearly distinguished in each friction master curve obtained at different loads. The load dependences of the friction peak positions in the master curves and in the friction versus temperature curves indicate that the heating effect is important at the sliding contact. All the results lead to a conclusion that the dynamic behavior of the PtBuA film is independent of the film depth and is the same as that of the bulk, showing no detectable enhancement of the molecular relaxation at the surface of the films.