1. Aircraft:
One of the most important inventions of the twentieth century was the birth of the airplane.
Since ancient times, human beings have dreamed of flying in space like birds. The kite invented by China people more than 2,000 years ago, although it can't take people into space, can be called the originator of the plane.
At the beginning of this century, there were two brothers in America, who made great contributions to the history of aircraft development in the world. They are the Wright brothers. At that time, most people thought that it was absolutely impossible for an airplane to fly by its own power, but the Wright brothers did not believe this conclusion. From 1900 to 1902, the two brothers made more than 1000 gliding test flights, and finally in 1903, they built the first manned aircraft "Flyer" 1.
Therefore, they won the honorary award of 1909 from the US Congress. In the same year, they established Wright Aircraft Company. This is a great success in the history of aircraft development.
2. Submarines:
1775, after the North American War of Independence broke out, the British colonial rulers relied on their maritime superiority to assemble a large number of warships and bombed the US navy and army in turn, causing heavy casualties to the US military.
At that time, there was a general named David bushnell in the American army. He couldn't stand being bullied by the British and was determined to fight back. He has been thinking hard: how can we sink the enemy ship? From the air, inaccessible; You can't hide from the water.
Once, when he walked to the reef by the sea, he suddenly saw a big fish dive under a small fish, jumped up suddenly and bit a small fish. He was greatly inspired by this "naval battle": Can he build a ship like a big fish and dive into the bottom of a British warship unnoticed and sink it?
Fish float and sink freely in the water by the swim bladder. Can a boat imitate a swim bladder? Starting from this idea, bushnell and military experts have successfully developed a motorboat that can sneak underwater. The bottom of the boat is a water tank similar to a swim bladder. There are two pumps in the water tank. When the ship sinks into the water, it will fill the cabin with water. When the ship is about to rise, it will press air into the water tank and discharge the water in the ship. Imitating the fin, two propellers are installed, one is forward and backward, and the other is up and down.
The motorboat skillfully subdued the British warship on its first voyage and was blown upside down. After gradual improvement, it has become a modern submarine.