周末,小明骑着自己的变速山地车去兜风。车轮与地面摩擦的沙沙声和耳边呼呼的风声,让小明十分陶醉。他低头看了一下车上的测速表,显示此时车速为45 km/h,即12.5 m/s。“速度也太快了,”小明有些怀疑,“是不是测速表不准确呀?”爱好物理的他准备用实验测测这个测速表到底准不准。说干就干,小明请来小华当助手。他们找来了细棉线、红毛线、 Weekend, Xiao Ming riding a variable speed mountain bike to go for a ride. The friction between the wheels and the rustle of the ground and the sound of the whirring of the ear, let Xiao Ming very intoxicated. He looked down at the speedometer on the car, showing a speed of 45 km / h, or 12.5 m / s. “Speed ​​is too fast, ” Xiao Ming some doubts, “Is not the tachometer inaccurate?” "He is prepared to experiment with the physics of the tachometer in the end is not allowed. To do, Xiao Ming, please come to Xiaohua as an assistant. They got a fine cotton thread, red wool,