Which type of gear is used specifically to change the direction of motion or to increase torque?

The bevel gear is specifically designed to change the direction of motion, typically at a right angle. It consists of conical-shaped gears that mesh at an angle, allowing the input shaft's rotational force to be redirected to an output shaft. This capability makes bevel gears particularly useful in applications where space constraints or specific alignment are a concern, such as in differentials in vehicles.

While other types of gears serve various functions—like the spur gear for simple direct motion and the helical gear for smooth and quieter operation—the bevel gear's unique design directly addresses the need for directional change while also being capable of increasing torque when properly utilized in a gear train setup. This makes it a versatile choice in mechanical systems requiring both motion redirection and increased force transmission.