What is the purpose of a universal joint?

• A. A joint that allows a drive shaft to move at different angles.
• B. A joint that rotates only in 90-degree increments.
• C. A joint made from a worm gear.
• D. A joint that can be found only in spacecraft.

Answer: (A)

A universal joint lets two shafts transmit rotation even when they are at an angle to each other, accommodating bending from things like suspension and steering while still turning. It uses a cross-shaped piece and yokes that lets the shafts articulate as they rotate, so torque can be transferred despite misalignment. Because the angle between the shafts changes during operation, a single universal joint can cause the output speed to vary; in many drivetrains this is mitigated by using two joints in phase or by a different type of joint, like a CV joint.

This isn’t about rotating in fixed 90-degree steps, it isn’t made from a worm gear, and it isn’t exclusive to spacecraft.