Final answer:
The force of static and kinetic friction between the two boxes depends on the normal force and the coefficients of friction. The coefficients of friction determine the force required to start and maintain motion between the two boxes.
Step-by-step explanation:
When a large box of mass m is moving on a horizontal surface at speed v0, and a small box of mass m sits on top of the large box, the coefficients of static and kinetic friction between the two boxes are μs and μk, respectively.
The force of friction between the two boxes depends on the normal force and the coefficients of friction. The normal force is equal to the weight of the small box plus the weight of the large box. If the normal force exceeds the maximum static friction, the small box will start sliding. Once the small box starts sliding, the force of friction becomes kinetic friction.
The coefficients of static and kinetic friction can vary depending on the surfaces in contact. The coefficient of friction is a unitless quantity with a magnitude usually between 0 and 1.0. The coefficient of friction affects the force required to start and maintain motion between the two boxes.