Cao Chong's modeling method is the concrete application of buoyancy principle. In the history of China, it is recorded that there is a similar story earlier than that of Cao Chong. In the Eastern Zhou Dynasty, Zhao Yan (reigned in 3 1 1-279 BC) had a big pig, and he ordered his ministers to weigh it with a steelyard. As a result, ten scales were broken, and the pig was not weighed yet. He also ordered the water officer to weigh it.
Besides weighing things by boat, it is also an invention of China people to lift things by boat. According to historical records, Pujinqiao is a pontoon bridge. It uses ships as docks and boards between ships as bridges. In the 12th year of Kaiyuan in Tang Dynasty (724), eight iron oxen were added as shore posts in order to reinforce the piers of ships and maintain the huge cables on both sides. Each iron cow weighs tens of thousands of kilograms.
During the Song and Qing Dynasties (1041-1048), bridges were destroyed and tens of thousands of catties of iron cows were washed into the river. After the bridge was destroyed for more than 20 years, Huaibing, a monk in Calm County, put forward the idea of salvaging iron cows and rebuilding Pujinqiao.
Huai Bing was a great engineering mechanic in the Middle Ages. His buoyancy lifting method was used by Italian mathematician Cardin (150 1- 1576) to salvage sunken ships in the 6th century.
At that time, the soldiers and monks sent people with good water to dive to the bottom of the water to find the place where the iron cow sank. He also had two big wooden boats hung side by side, and the wooden boats were full of sediment. A shelf was set up between the two wooden boats. Huai Bing personally led people to row two wooden boats full of sediment to the place where the iron cow sank. He also asked people familiar with water conditions to dive to the bottom of the water with ropes and tie the iron cow with ropes. The rope was tightened and the other end of the rope was tied to two boats.
After the preparatory work was completed, Huai Bing ordered people to throw the sediment from the ship into the river, and the sediment was shoveled into the river. The ship slowly rose and finally pulled the iron cow out of the mud. Huai Bing also ordered people to row the boat to the place where the pontoon bridge was built, and two big boats dragged the iron cow out of the water back to its original position.
Each iron cow weighs tens of thousands of pounds. Why can Huai Bing pull the iron cow out of the mud at the bottom of the river?
The two wooden boats were originally filled with sediment. The sediment is heavy, and the draft of the wooden boat is deep, which means that the wooden part displaces a lot of water and has great buoyancy. According to the ups and downs of the object, the buoyancy of the wooden boat at this time is equal to the weight of the boat plus the gravity of the sediment. When the sediment is thrown into the river, the sediment on the ship decreases, and the buoyancy of the two wooden boats exceeds the weight of the ship plus the gravity of the remaining sediment. At first, the boat didn't float, because with the sediment being thrown out of the wooden boat, the potential force of the rope on the iron cow became more and more great, until the excess buoyancy exceeded the gravity of the iron cow in the water and the action of mud and river water on the iron cow, and the iron cow was gradually pulled out of the mud.