A $50\text{ kg}$ wooden crate rests on a flat horizontal concrete floor. The coefficient of static friction between the wood and concrete is $\mu_s = 0.4$. A worker pushes the crate horizontally. What is the minimum horizontal force required to start the crate moving?

A block of mass $m$ is placed on an adjustable inclined plane. As the angle of the incline $\theta$ is slowly increased, the block begins to slip when the angle reaches $30^\circ$. Determine the coefficient of static friction $\mu_s$ between the block and the plane.

A tall refrigerator of height $H = 2\text{ m}$ and width $W = 0.8\text{ m}$ rests on a floor with $\mu_s = 0.6$. Its center of gravity is exactly in the middle. A person pushes horizontally at the very top edge of the fridge. Will the refrigerator slip first, or tip over first?

Civil engineers use the principles of friction extensively when designing gravity retaining walls used to hold back soil. Explain how friction at the base of the wall prevents structural failure, and what engineers do if the natural friction is insufficient.

In automotive engineering, Anti-Lock Braking Systems (ABS) prevent tires from locking up and skidding during hard braking. Relate the function of ABS to the fundamental difference between static and kinetic friction.