A friction motor is a simple mechanism to propel toy cars, trucks, trains, action figures and similar toys. The motor consists of a large

flywheel A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, as ...

which is connected to the drive wheels of the toy via a very low

gear ratio A gear train is a mechanical system formed by mounting gears on a frame so the teeth of the gears engage. Gear teeth are designed to ensure the Pitch circle diameter (gears), pitch circles of engaging gears roll on each other without slipping, pr ...

, so that the flywheel revolves faster. The flywheel's axis is perpendicular to the direction in which the toy faces and moves. When the toy is pushed forward, the drive wheels engage the flywheel. Pushing the vehicle forward repeatedly spins this flywheel up to speed. When let go, the flywheel drives the vehicle forward. The flywheel stores the kinetic energy of the initial acceleration and propels the toy after it is released, by forcing the perpetual motor that revolves the kinetic energy. As the flywheel, unlike the spring of a

pullback motor A pullback motor (also ''pull back'' or ''pull-back'') is a simple clockwork motor used in toy cars. A patent for them was granted to Bertrand 'Fred' Francis in 1952 as a keyless clockwork motor. Pulling the car ''backward'' (hence the name) win ...

, is continuously rotating and not held, the motor may be "pumped up" by pushing the car repeatedly forward. The cars also typically work in forward and reverse. Some used a ''zip cord'' pulled from the vehicle body to accelerate the flywheel directly. Another system was the ''Turbo Tower of Power'' (TTP) in which air expelled from a hand-operated pump pushed turbine blades on the flywheel's rim. These toys were especially popular in the 1960s to 1980s though they continue to be available today.

References

Toy cars and trucks Mechanical toys {{Toy-stub