Banked curve
Definition
A banked curve is a road or track tilted inward so part of the normal force points toward the center, helping vehicles turn without relying only on friction.
Technical definition
On a curve of radius r banked at angle θ, the horizontal component of the normal force N·sinθ provides centripetal force; the ideal speed with no friction needed is v = √(gr·tanθ).
Example
A highway exit ramp of radius 100 m banked at 15° has an ideal speed of √(9.81×100×tan15°) ≈ 16 m/s (≈58 km/h) — at that speed a car needs no friction to hold the turn.
Common confusion
Banking does not eliminate the need for friction at all speeds — it only removes it at one ideal speed. Go slower and you slide inward; go faster and friction must grip outward, which is why icy banked ramps are still dangerous.