The speed of badminton is not only related to its own weight and speed, but also affected by temperature, humidity, altitude and other factors. Generally speaking, the higher the altitude, the higher the temperature and humidity, and the lighter the weight of the ball. Because the higher the altitude, the higher the temperature, the smaller the air density, the smaller the air resistance when badminton flies, and the faster the ball will be. It's time to use a lighter (slower) ball. Under such circumstances, it is necessary to choose a lighter ball. On the other hand, the lower the altitude, the lower the temperature, the greater the air density and air resistance, and the slower the speed of the ball. Therefore, badminton used in low altitude and low temperature areas is heavier. When the air humidity is high, the water content of feathers will also increase, which will lead to the increase of the weight of the ball and the speed of the ball. So the higher the humidity, the lighter the ball used. According to referee Lei Mingji, last year's World Youth Championship held in Guadalajara, Mexico, used the YONEX ball of 1 that he had seen for the first time in his life. Because the altitude there is as high as 1800 meters, the air is thin and the air resistance is small, so the ball chosen is relatively light.