PURPOSE: To demonstrate the effect of locked wheels on vehicle stability.
DESCRIPTION: With both sets of wheels free, push the car across the floor; it moves in a straight line with the orientation in which it was pushed. With the front wheels locked, it will also continue in the normal forward orientation. With the rear wheels locked, however, when pushed in the forward direction it will rotate so that it moves backward. Because rolling (static) friction is greater than sliding friction, whichever set of wheels is sliding will end up in the forward direction.
REFERENCES: (PIRA 1K20.40) See Demonstration Reference File for several articles on automobile stability when the rear brakes lock.
EQUIPMENT: Toy car, tape to lock wheels.
SETUP TIME: None.
Go back to Lecture-Demonstration Home Page.