You probably think of wet surfaces as being slippery. Surprisingly, the opposite is true for human skin, as you can demonstrate by sliding a dry versus a slightly damp fingertip along a smooth surface such as a desktop. Researchers have found that the static coefficient of friction between dry skin and steel is 0.27, while that between damp skin and steel can be as high as 1.4. Suppose a man holds a steel rod vertically in his hand, exerting a 400 N grip force on the rod. What is the heaviest rod he can hold without slipping if

a. His hands are dry?

b. His hands are wet?