Which gear configuration includes a gear on top of a rack?

The correct answer is indeed the configuration that involves a gear on top of a rack, known as rack and pinion gears. In this system, the pinion is a small gear that meshes with a straight "rack" — which is a flat strip of metal that has teeth similar to a gear. When the pinion wheel rotates, it moves along the length of the rack, converting rotational motion into linear motion.

This type of gear arrangement is commonly used in applications such as steering mechanisms in vehicles, where the rotational movement of the steering wheel (pinion) translates into the linear movement of the car's wheels (rack). The efficiency and direct conversion of motion make rack and pinion gears particularly effective for applications requiring precise control over linear movement.

Other gear configurations, such as planetary gears, bevel gears, and helical gears, serve different purposes and do not involve the specific interaction between a gear and a rack. Planetary gears typically consist of a central sun gear surrounded by smaller planet gears that rotate in an orbit. Bevel gears are designed to change the direction of motion between intersecting shafts, while helical gears are designed for efficiency and to transmit power between parallel shafts. Each of these configurations has its unique design and application, distinct from the