In an improved design of a thrust bearing, the bearing surfaces are shaped like:

The correct answer is that the bearing surfaces in an improved design of a thrust bearing are shaped like pads free to tilt. This design is important because when a thrust bearing is subjected to loads, the surfaces can experience misalignment and uneven distribution of forces. Pads that are able to tilt allow for better load distribution across the bearing surface, which helps to minimize wear and reduce stress concentrations.

By allowing the pads to tilt, the design accommodates slight misalignments that may occur due to thermal expansion, manufacturing tolerances, or operational conditions. This capability to adjust means that the bearing can maintain a larger contact area, leading to lower friction and improved overall performance. Additionally, tilting pads can also help to accommodate vibration and dynamic changes in load, enhancing the durability and lifespan of the bearing.

Other designs, such as flat plates or fixed pads, do not have this advantage as they can lead to increased wear and potential failure under varying load conditions. Spheres may also provide a unique contact surface but do not effectively manage the load distribution in thrust applications. The tilting pads represent a crucial advancement in thrust bearing technology, making them a widely adopted choice in engineering applications where reliability and efficiency are paramount.