Which mechanism converts rotary motion into linear motion?

The screw jack is a mechanical device that effectively converts rotary motion into linear motion through the principle of a screw. When the handle of the screw jack is turned, the rotational movement causes the screw to advance or retract along its thread. This movement translates directly into linear displacement along the axis of the screw, allowing for lifting or lowering of a load.

This mechanism is widely used in various applications where controlled vertical movement is required, such as in lifting heavy objects or adjusting the alignment of machinery. The efficiency of this conversion of motion is due to the helical design of the screw, which allows for significant mechanical advantage with relatively little manual effort.

In contrast, while gear systems primarily transmit rotary motion between shafts, they do not inherently convert that motion into linear movement. A pulley system changes the direction of force and can facilitate lifting but does not create linear motion from rotary motion in a direct manner like the screw jack. Friction drives transmit motion through contact but do not govern the conversion between rotary and linear motion explicitly. Therefore, the screw jack stands out as the correct mechanism for this specific conversion of motion.