The first condition for friction to occur is for two objects to be in contact. There are two ways of contact, one is surface-to-surface contact, and the other is point-to-surface contact. The first method is like rubbing hands, which has high frictional resistance and generates a lot of heat. This method is called sliding friction. The second method is like rolling a ball on the ground, with low frictional resistance and fast rolling speed. This method is called rolling friction. Secondly, the material of the contact surface and the weight of the moving object will also affect the frictional resistance, which we will talk about later.

Let's get down to business, the previous nonsense is to elicit today's theme, we want to talk about the development history of bearings. As for who invented the first bearing, the academic circles hold different opinions, and I do not make comments. The past is a story, just listen to it, and don't be too entangled.

First of all, the ancestors gradually figured out the law of friction in their lives. For example, dragging prey or a large rock on the ground can be very laborious, but if you arrange logs under the prey or rock, it will be very easy to drag. This seemingly simple improvement is actually a major progress in the history of human development, indicating that human beings have discovered the secret of friction, which can convert sliding friction into rolling friction, so as to achieve the purpose of saving labor.

During archaeological excavations at the site of Nineveh on the Mesopotamian plain, archaeologists discovered a fresco (picture 1) in one of the tombs, depicting the carrying of a huge Stone statue scene. It can be seen from this that the huge stone statue seems to be placed on a 'boat'. There are two places on the front and back of the 'boat' for fixing the traction rope, and the people drag the traction rope to move the statue. It is worth noting that there are some logs scattered under and around the 'boat'. It is conceivable that these logs are actually used as sleeper rails to reduce frictional resistance.

The above method of using logs as sleeper rails to transport heavy objects is similar to the plane needle roller bearings we are still using ( figure 2). The so-called plane needle roller bearing is to fix the needle roller through the cage. This kind of bearing is usually placed between two planes, which can convert the sliding friction between the surface and the surface into the rolling friction between the point and the surface.

However, this kind of plane bearing is quite different from the bearing we usually recognize. Most people would think that the bearing should be circular and allow for rotational motion. This view may be more representative, so when did this kind of bearing first appear? There are several different views here, and I will briefly introduce them. First, it is believed that the earliest bearing should be the axle bearing used on the axle of the carriage, which can be corroborated from some archaeological discoveries. Second, it is believed that there are certain differences between ancient axle bearings and modern bearings in structure. Considering the similarity in structure, the bearings used in 'Jianyi' are closer to modern bearings. 'Jianyi' is a kind of astronomical observation instrument in ancient my country. Its inventor is no longer known, but the production of lemon guns is respectful. You can find a very detailed introduction on the Internet, so I won't say much here.