Passage V

A block is placed on an inclined plane, as shown in Figure 1.

The angle of inclination is increased. The angle at which static friction is overcome and the block starts to slide is α_c, the critical angle for sliding. The amount of static friction to be overcome depends on µ, the coefficient of static friction.

Table 1 gives α_c and µ for a steel block sliding on various uncoated surfaces at 20°C. Tables 2 and 3 give α_c and µ for the steel block sliding on a steel surface coated with various oils at 20°C and 100°C, respectively.