Selected Works of the National Youth Science and Technology Innovation Competition Selected Works of the National Youth Science and Technology Innovation Competition (II) (Paper) Research on the Friction Direction of the Front and Rear Wheels of Bicycles Xu (National First Prize), Instructor of Huangshi No.7 Middle School, Hubei Abstract: In the research study class, under the guidance of Mr. Xu, I conducted an experimental study on the friction direction of the front and rear wheels of bicycles. After repeated experimental exploration and thinking, I summed up six interesting and effective judgment methods and fully realized the direction of friction and relative movement. Bicycles can move forward by friction on the ground. To understand the principle of cycling, we must first understand the friction between the ground and the wheels when we ride a bicycle in a straight line. What method can be used to judge the friction direction between the ground and the front and rear wheels of the car? In the research-based learning class, we have conducted many experimental studies on this subject. The following are several experimental judgment methods that we have summarized, which are very interesting and effective. First, the judgment method of slip point. In cold winter, let the bike run on the ice. Because the ice is very smooth, it is difficult for the car to move forward, just slipping in place. We found that before the car fell, only the rear wheel slipped in place, but the front wheel did not spin and slip. It can be seen that the rear wheel is actively "rubbing" the ground backwards, so the direction of friction between the ground and the rear wheel is forward; Only when the bicycle moves forward, the ground "actively" rubs the front wheel, and the front wheel can turn. It can be seen that the friction facing the front wheel is backward. Second, the "blocking in the sand" judgment method allows a classmate to ride a bicycle in the long jump bunker on the playground. Because the sand is deep (about 15cm), the wheels will get stuck in the sand and it is difficult to drive. When the car stops moving forward, because the rider continues to pedal hard, the rotating rear wheel throws the sand behind it backwards, indicating that the direction of friction between the rear wheel and the ground is backward. According to Newton's third law, facing the rear wheel, of course. We also observed that the front wheel did not turn after the car was blocked, so it was different from the rear wheel: when the bicycle was running, the front wheel was subjected to friction from the ground in the backward direction. Third, the "tape curling" judgment method firmly sticks a piece of medical tape on the outer side of the front and rear rubber tires of the automobile (the parts on the tires that can repeatedly touch the ground). After the bicycle travels forward for a certain distance, we check the adhesive tape and find that the adhesive tape attached to the rear wheel curls at the first end touching the ground, while the adhesive tape attached to the front wheel curls at the last end touching the ground. As you can imagine, because the ground has a forward friction on the rear wheel and a backward friction on the front wheel, this is the result. Fourth, the "Acrobatic Association" judges that acrobatic masters can make the front wheels fly and only rely on the rear wheels to land. As long as he keeps stepping on the pedal, the car will move forward and even accelerate. Obviously, the friction on the rear wheel is forward. But if the rear wheel flies and the front wheel hits the ground, even if he keeps pedaling, the bicycle will slowly stop, which shows that the friction facing the front wheel is backward. It should be noted here that there are two different situations because the pedal axle chain is connected with the rear axle. V. Design idea of "long" hair of the wheel If you drag the hairy side of the soft brush down on the desktop, the direction in which the soft brush falls can indicate the direction in which the brush is rubbed. Imagine that the front and rear wheels of a bicycle are covered with a circle of short fluff. In which direction will these fluff fall under the action of ground friction? As you can imagine, the lodging direction of a circle of hair on the front wheel is opposite to that of the rear wheel, as shown in figure 1. Is the experimental result consistent with figure 1? (In this paper, for the convenience of description, the hair lodging direction of the rear wheel is called clockwise, and the hair lodging direction of the front wheel is called counterclockwise. ) 1. We glued two small pieces of fur to the front and rear wheels of the bicycle clockwise with all-purpose glue. After riding for a while, I found that the clockwise hair of the rear wheel was still obedient, while the original clockwise hair of the front wheel was not so obedient. 2. We use all-purpose glue to stick two small pieces of fur on the front and rear wheels of the bicycle in a counterclockwise direction. After riding for some distance, I found that this time, the anti-clockwise hair on the front wheel was obedient, but the anti-clockwise hair on the rear wheel was not so obedient. The results of two experiments confirmed the result of imaginary number 1, indicating that the front and rear wheels of the bicycle were subjected to ground friction in the backward and forward directions respectively. Sixth, observe the ordinary bicycle by the direct judgment method of "driving wheel and driven wheel". The rear wheel is the driving wheel (connected with the chain of the pedal shaft), which can rotate "actively" and is the "power source" to make the bicycle move forward. The front wheel is a driven wheel, which is "forced" to rotate and plays the role of auxiliary driving and balance. The ground friction direction on the driving wheel is the same as the vehicle direction (forward), and the ground friction direction on the driven wheel is opposite to the vehicle direction (backward). The above six methods are obtained through our own observation and experiments in the process of carrying out research activities. In a similar way, we also studied the direction of ground friction between front and rear wheels and the direction of ground friction between front and rear feet when driving. And fully realize that the direction of friction is opposite to the direction of relative motion or relative motion trend. It is interesting and effective to carry out research-based learning. It is much better for students to use their brains and think positively than to sit in the classroom and just listen to the teacher. Our thinking ability and innovation ability have been greatly improved. Note: Xu Jingjing from Huangshi No.7 Middle School was recommended to Wuhan University in 2004, majoring in applied physics.