Which tool/application takes advantage of both high and low friction?

The belt sander is the correct choice because it effectively utilizes both high and low friction in its operation. A belt sander consists of a rotating belt that is coated with an abrasive material. When the sander is in use, the portion of the belt that makes contact with the surface being sanded creates high friction, which removes material from the surface, allowing for effective smoothing and shaping.

On the other hand, the belt itself is designed to move smoothly over pulleys and other components of the sander, which requires lower friction in those areas. This combination allows the tool to operate efficiently—removing material while ensuring that the belt can move freely without excessive resistance.

Other tools listed do not have the same operational dynamic involving both high and low friction. For instance, a screwdriver generates primarily high friction between the tool's tip and the screw head but does not have the dual friction aspect that the belt sander exhibits. A pulley system generally relies on low friction for efficient movement, while a geared mechanism focuses more on transferring torque with controlled motion rather than actively engaging both high and low friction in a single operational context.