Chapters 8 and 9

Friction and Moment of Inertia

Dry Friction

 Friction forces exist between two rough surfaces act on a body to appose its tendency of motion.

 When a static fiction approaches a maximum value, motion between the contact surfaces is impending.

Fs = 𝜇 s Ns Fs = Maximum Static Friction Force.

𝜇 s = coefficient of static friction.

 If slipping occurs, then the friction force remains constant and equal to: F k = 𝜇

k

N; 𝜇 k = Kinetic friction constant.

Tipping of a slender objects such as crates

Moment of Inertia

 Area Moment of Inertia represents the second moment of the area about an axis.

 Its used in formulas related to the strength and stability of structural and mechanical members.

 To determine the moment of inertia of irregular area, a differential element is selected and then integration of the entire area is performed.