Which mechanism converts rotational motion into linear motion by engaging a straight rack with a rotating pinion?

• A. Rack and Pinion
• B. Crankshaft and Rod
• C. Cam and Follower
• D. Lead Screw

Answer: (A)

A straight rack being driven by a rotating pinion is a rack and pinion setup. When the pinion turns, its teeth mesh with the rack teeth and push the rack along in a straight line. The gear teeth are matched so each full turn of the pinion moves the rack by a precise, predictable distance, giving smooth and controllable linear motion. This arrangement is common in steering systems and linear actuators because it’s simple, compact, and efficient. The other mechanisms don’t fit this description: a crankshaft and rod use a crank to convert rotation to back-and-forth linear motion but without a straight rack; a cam and follower drives a follower in a curved path; a lead screw translates rotation to linear motion via screw threads, not by meshing with a rack.