Newton’s laws & circular motion — what actually pushes a car around a bend
“Candidates did not appreciate that the forces… involve a Newton’s Third Law action–reaction pair… Only a minority understood that the centripetal force was provided by friction otherwise the car would continue in a straight line. Many argued that friction was required to balance the centripetal force… Many correctly identified less friction in wet weather but concluded θ would need to be smaller rather than greater.”
Top view. The car needs mv²/r of inward force to hold the circle; the road can supply at most μmg of friction. Raise the speed or make it rain and watch what Newton’s first law does.
On a banked road part of the normal force helps push inward, so less friction is needed — which is why, in wet weather, the banking angle θ would need to be greater, not smaller (the part (e)(iii) conclusion most candidates inverted).
Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H1 Physics 8867 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.
Made by lookang, using Claude Fable 5. More resources: iwant2study.org