Coefficient of static friction?

Three same size boxes A, B and C have different coefficient of static friction sliding over a table. Box A having a smooth surface with mass m, box B having a rough surface with mass m while box C having a rough surface with mass 2m. Which box has the largest coefficient of static friction?


Does the coefficient of static friction change if there is a water layer between the boxes and the table? Does the stopping distance change?





Please make it plain that I can easily understand, thanks a lot!

Coefficient of static friction?
friction force= coefficient x reaction force





F=cR





F=friction force


c=coefficient


R=reaction force





coefficient only influenced by the conditions of the surface, not the area and weight.





so the 1st question i cannot answer cause the information not enough. i cannot compare based to their friction force.





2nd question, sure the coefficient will change.





logical thinking, when there is a watery layer, sure the friction force will decrease.


seen the reaction force remain the same.


(reaction force= mass of object x gravitational force constant)





so, coefficient will decrease.





seen the friction force decrease, the stoping distance become longer.


we need more distance to stop seen the friction is weak.





thanks...