Friction toys are driven by springs or a friction motor. This is a simple mechanism to propel toy model tin trains, cars, action figures, and other toys. The motor consists of a large flywheel which is connected to the drive wheels of the toy via a very low gear ratio, so that the flywheel revolves faster.
The drive spring of, for example, a friction-driven toy car is wound when the back wheels of the car are pushed backwards against a high-friction surface. Carpet, or even a wood floor, can work very well as a friction source, spinning the wheels backward and winding the spring. Glass or a wet surface work less well, failing to provide enough friction to move the wheels. In essence, the wheels and axle of a spring-driven friction toy car are being used in the same way as a winder for an old mechanical clock.
While many spring driven toys require a cog or series of cogs to change the direction of the force of the winder or the force of the spring, a simple friction toy car seldom needs any cogs. The axle serves as a spool to wind the spring; the backward friction rotates the axle to wind the spring. When the car is released, the spring unwinds again, spinning the axle forward and propelling the car. This use of a spring lacks elegance and control but is delightfully easy to understand.