Take a car around a banked curve and find the fastest safe speed before it skids. Tilt the road, add friction, and watch the normal force, friction and the required centripetal pull rebalance — or flip to a conical pendulum swinging the same physics on a string.
Try this: raise the bank angle and the safe-speed window widens — at exactly the ideal speed v₀ you need no friction at all (the friction arrow vanishes). Push past v_max and the track turns red as the car skids outward.