When discussing the manufacture of wheels, Kao Gong Ji Lun Zhang Ren talked about the relationship between the shape of wheels and the speed of movement from factors such as stress, movement and different influences of contact with the ground, saying: "Every method of observing cars is meticulous, and there is no speed." "Micro-touch" means that the contact area between the wheel and the ground is very small. In other words, if the wheels have less contact with the ground, they will easily turn fast. So, how can we achieve "micro touch"? It goes on to point out: "If you want to minimize it and you have nothing to take, just take it." That is, make the wheels as round as possible. This is an empirical summary of the relationship between rolling speed and contact area of rolling elements in practice, which accords with modern friction theory. When discussing how to check whether all parts of the wheel are uniform, it said, "spokes must be uniform, and leveling (sinking) must be uniform." "Water is considered (depends on) its calmness." Here, water is immersed in water. If "leveling" means that the ups and downs are consistent, then all parts of the wheel must be uniform and meet the requirements of making wheels. This is the application of buoyancy principle in manufacturing wheels. When discussing the influence of wheel size on pulling force (cattle or horses), it said: If the wheel is too short, the horse will always go uphill. From the current mechanical knowledge, when the wheel is too low, the axle is at a certain angle with the ground, and the horse has to bear some gravity besides overcoming the motion resistance, so the horse always struggles like going uphill. This is an excellent analysis of the stress on the inclined plane in practice.
"Kao Gong Ji" also analyzed the technology related to ballistics. It said in "Arrow Man": "Water can distinguish its yin and yang, determine its ratio, clip its ratio to determine its feather, participate in its feather and determine its blade. Even if there is an explosion, you can be afraid. " That is to say, in order to keep the arrow stable in flight, the feathers on the arrow are symmetrically arranged according to a certain proportion, and the arrow is added, so that it is not afraid of the influence of the wind in flight. Then he said, "The former is weak, the latter is weak, the latter flies, the middle is weak, and the middle is strong." "Feather abundance is late, and feather killing is late." This shows that if the arrow shaft is light before heavy, or heavy before light, it will affect the flying height; Improper configuration of intermediate weight will affect flight stability; Too many feathers make the flight slow. If there are too few feathers, the arrow can easily fall to one side and miss the target.
Gong Ji was the first person to discuss the inertia of objects. The article "One Man" said: "I advise you to increase your horsepower. When it runs out, you can take it." It means that when pulling a horse, the horse has stopped exerting its strength, but the car can still go far. This paper points out a basic property of an object-inertia, which is also the earliest discussion on inertia phenomenon in the world.
On the basis of carefully observing the movement of objects in the Eastern Han Dynasty, Wang Chong pointed out the reasons why people's vision will have illusions when observing the speed of object movement and how to measure the speed of object movement in Lun Heng. In Lun Heng, he said: "Heaven is ill, and people go too far, so it is too late. Looking at the distant things, if he doesn't move, if he doesn't move; How to test? Take a boat in the river and sea, driving the wind, getting sick near the shore, getting off the shore late, getting stuck, getting sick or late, being far and near is natural. " That's because the distance between the observer and the moving object is different, so its speed is also different. This also shows that Wang Chong already knows the influence of different viewing angles on the speed of observing objects. On the speed of movement, there are also "thousands of miles in the day, thousands of miles in the night, and thousands of miles in the unicorn, but the day is similar to the unicorn step." It means that the sun and Kirin move at the same speed during the day, which shows that the concept of "speed" in modern physics has sprouted.
Regarding the relationship between force and motion, Wang Chong said: "Therefore, the vehicle travels on land and the ship travels in the ditch. Those who are full and heavy are late, and those who are empty and light are sick. " "The responsibility is great and it is difficult to make rapid progress." He also said that "the ancients had much strength and physical load of thousands of miles." You can almost stretch the hook and let it bootstrap. Can't leave the ground. "Obviously, not only do you know that under the action of external force, if the external force is constant, the heavier the object, the more difficult it is to start moving or change the state of motion. This is obviously the germination of Newton's second law of motion, and it also acknowledges the fact that internal forces can't change the motion state of objects.
The leaky armillary sphere and the seismograph were made by Zhang Heng in the Eastern Han Dynasty (AD 78- 139) according to the principles of physics and mechanics. They played a role in astronomical phenomena and earthquake observation respectively. The leaky astrolabe is an instrument for automatically measuring and displaying astronomical phenomena. It uses a hollow copper ball to represent the celestial sphere. The copper ball is painted with constellations, ecliptic and equator, and the horizon ring and meridian ring attached to the celestial sphere. The celestial sphere can be supported on the meridian ring and rotated around the celestial axis. In addition, the broken kettle measuring time is linked with the elephant, that is, using the isochronism of the broken kettle, taking the water leaked from the broken kettle as the power, and then using the gear installed in the elephant as the transmission and control equipment, the elephant rotates around the celestial axis at a constant speed every day, so as to achieve the purpose of automatically and almost correctly demonstrating the celestial phenomena. Hou Feng Seismograph is made of fine steel, which looks like a statue of wine, and there are eight "Capital Columns"-columns with thick top and thin bottom. Because of the high center of gravity, it is very easy to fall in the direction of vibration when the ground vibrates. There are eight dragons with small copper balls in their mouths. Under each dragon's head, there is a toad with its mouth open (see Illustration 5). A capital pillar fell down, driving the connected dragons to open their mouths, and the copper balls inside fell into the mouth of the toad below. Therefore, the direction of the earthquake can be judged by observing the direction of the falling copper ball.
In the concept of relativity of motion, the astronomer of Jin Dynasty (26 1 ~ 303) said: "Take a boat to wade, the water will go, but the boat will not move" (Records); Jin (283 ~ 363), whose name is Bao Puzi, said in "The Inner Chapter of Bao Puzi, Senan": "The cloud goes west and the moon goes east." This idea of relative motion is even used to explain the motion of celestial bodies in Eleven Days in the Book of Jin: "The sky turns left like a millstone, the sun and the moon turn right, and turn left with the sky, so the sun and the moon actually move eastward, while the sky pulls westward." For example, an ant walks on a millstone, grinding his left hand, and the ant walks to the right. When the sick ant comes late, he has to take the millstone back to the left. "Very valuable is the book Shang Shuwei's Examination of Ling Yao, which was written at least in the Eastern Han Dynasty (the author is unknown and included in the book Gu Wei compiled by Sun Yi in the Ming Dynasty). At the same time, the book puts forward a famous conclusion: "There are four tours on land, from winter to day, going north to Wan Li in the west, and from summer to day, going south to Wan Li in the east, and the spring and autumn equinox is one of them. "About this view of the theory of relativity of motion, Ling Yao was at least about 1500 years earlier than Galileo's dialogue. This view shows that China's ancient sports thought has reached a high level.