Algodoo

A few different principles demonstrated by gears

Gear reduction: planetary gears in this configuration results in a significant reduction in speed, and also increase in torque

A 10- tooth gear meshed to a 35 tooth gear, a reduction of 3.5:1 Operated by arrows

Flywheel + Starter (A and D to move arm, arrows to spin gear) a weighted disk keeps momentum going without the need for outside forces, for a period of time.