Friction toys, a class of toys both antique and collectable and modern and disposable, are driven by springs. The power needed to drive the toy is gathered in the spring and released in a variety of ways as the spring unwinds.
How The Spring Is Wound
The drive spring of 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.
No Cogs Needed
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.