1, Grade 8, Class 2, tug of war. After hard work, Class Two won by a narrow margin.

Tug of war should be understood as a process. The so-called weakness means that the speed of the rope is very low when it is displaced. It means that in the process of applying force to the rope by both sides, the unequal time of the forces is very short, but the unequal force produces acceleration, and the acceleration accumulates the motion speed. The so-called approximate stillness of the weak comes from here, that is, the force difference between the two sides is very short and very small. In the process, the rope moves at a low speed, which is almost uniform (the speed is generated, and the two forces remain equal, which makes the process almost uniform, which is considered weak, and may even slow down at the end, but this does not affect us to imagine the scene of uniform movement in the process). Newton's law has been learned, uniform or static, the external force is zero, and the two forces are in opposite directions and equal in size.

Pack up: At the beginning of tug-of-war, the two sides were still, 4,000 cows each other; At a certain moment, the force of 1 is less than 4000, which leads to acceleration A and short duration T, which makes the rope produce initial velocity V; At this time, the students in 1 class realized the danger and made decisive efforts, but they could only keep a balance with Class 2 at 4000. But because of the initial speed, the rope will continue to move at a low speed, and this weak speed accumulation led to the victory of Class 2. In this process, ignoring the extremely short time of force imbalance, both of them have reached force balance most of the time.