Dynamic sliding friction of pencil leads on dry and oiled glass inclines

The present work studied the dynamic sliding friction of pencil lead samples on inclined dry and oiled smooth glass plates. Four types of samples with different masses and lead hardnesses (4B and 4H) but identical diameters were used to vary the contact surface conditions. The results showed that the sliding velocity for a given angle increased as the mass of the sample increased; the velocity also increased as the hardness increased from 4B to 4H. To interpret the velocity change, the present study used an analytical model, which suggested that wear particles play a significant role in the dynamic friction on both dry and oiled surfaces.