In mechanical terms, a bearing is a machine element that facilitates smooth and controlled motion between two or more moving parts. It is designed to reduce friction and support the load generated by the moving components, allowing them to move relative to each other with minimal resistance. Bearings are crucial in a wide range of machinery and equipment, providing support for rotational, linear, and oscillating motion.

In summary, main bearings are primarily responsible for supporting the rotational motion of the crankshaft and withstanding radial loads, while thrust bearings are designed to counteract axial forces and maintain the axial position of the crankshaft. Both types of bearings play critical roles in ensuring the smooth and reliable operation of engines and machinery.