Spinback

A collection of gears attatched to a large base.

• Two cranks of different ratios allow control of the gear
• The relative massiveness of the main gear shows children a reaction - they must somehow hold the base to keep it from sliding over a carpet or floor.
• Marbles in a track within the wheel demonstrate that the same relationship that makes the base want to spin opposite of the gear works on a smaller scale - the marbles will at first be stationary, and gradually accelerate.
• The different gear meshing helps build an intuition for gears and directionality as well as mechanical advantage.
• Critics may argue that this gear represents serious danger in the risk of children's appendages getting caugh in the meshing of the gears. I'd argue that this actually teaches another very important physical lesson - avoidance of things that will hurt you. If more children were allowed to learn this lesson for themselves, my generation would be much more comfortable around tools and machinery, and many fewer bright orange caution notices would be printed on everything I buy.
• All the same, this toy is probably best targeted at older children.
• The base should be made of plastic so it has less inherent friction with the surface it rests on and to control weight of the whole item. The gears should be relatively massive so that the inertia they exhibit is noteworthy to the children.