Banked-curve friction direction depends on speed
- 01
The tempting model
Assuming friction always points up or down a banked curve regardless of speed.
- 02
Why it feels right
Friction gets memorized as 'opposes motion,' but the car is moving around the curve, not up or down the slope.
- 03
Where it breaks · how to catch it
You choose friction direction before comparing speed to the no-friction design speed.
- 04
The correct model
On a banked curve, friction opposes impending slipping along the surface. Below design speed the car tends to slide down the bank, so friction points up; above design speed it points down.
- 05
Repair · see it, then test it
worked example A car takes a banked curve slower than the no-friction speed. Which way does static friction point?
Tempting move
Down the bank because the car moves forward.
Correct move
Up the bank, preventing the car from sliding inward/downward.
Test the repair NL-18 · transferMake a fresh prediction before referring to the worked example.
Then practise it on the ladder
R14Banked curve speed regimesadds: Static friction direction on a banked curve depends on impending slipping.