Classical Mechanics (Kibble & Berkshire) · Problem 11.19
Lagrange's equations and conservation principles — T.W.B. Kibble, F.H. Berkshire
Physics — Mechanics · pile-of-balls
Problem
Pile of balls Three identical balls are placed in contact with each other on a horizontal table and a fourth identical ball is placed on top of the first three. Show that the four balls cannot be in equilibrium unless (i) the coefficient of friction between the balls is at least 3−2, and (ii) the coefficient of friction between each ball and the table is at least 41(3−2).