Analysis And Study On S-shaped Free Kick In Football

In the 154-year history of modern football, it has given birth to countless impressive goals, including one type, of which because of the special nature, the media and public opinion often use such a name to describe its bizarre--Violate the laws of Physics Goal,that is, S-shaped free kick. Because of the low frequency of the S-shaped free kick, there is few materials to study, so it is often overlooked in all kinds of study on free kick in football. This thesis collects and interviewed a large number of S-shaped free kick imaging and materials, explores the definition, principle and occurrence mechanism of S-shaped free kick, and puts forward training advice to provide the reference for related studies on S-shaped free kick.This thesis, based on Bernoulli's principle, Magnus Effect and Karman Vortex Street of hydromechanics defines S-shaped free kick by mathematic methods, derives and calculates formation mechanism and occurrence mechanism of S-shaped free kick; sums up and analyzes the characteristics of S-shaped free kick by watching the relevant video materials; using quantitative analysis method, through assigning values to relative factors of S-shaped free kick, further learns S-shaped free kick in details and reveals the formation and the motion law of S-shaped free kick scientifically and objectively via accurate assignment calculation and study to grasp the essence and clarify the relationship, as well as draws forecast trends and directions; with referring to literature at the same time, summarizes the frontier of the fast strength training theory of lower limbs and the successful experience of excellent athletes, thus to provide feasible suggestions for the training of S-shaped free kick.Study Conclusions:1) The basic principle of S-shaped free kick formation is Karman Vortex Street. When Reynolds number between 3x105 and 3x106 in the process of football flight, the formation of the nonlinear Vortex Street behind the football is the essence of S-shaped free kick formation.2) S-shaped free kick formation requires two necessary conditions. The first is irrotional condition, which means controlling the football in the process of flight almost without producing the angular velocity on the cross section when hitting the ball; the second is high speed condition, that is, there must be a time slice in the process of football flight, in which the football velocity scalar is not low than "escape velocity Vmin",and the length of the time slice decides the significance of S-shaped trajectory.3) Taking the condition with normal atmospheric pressure and 20 ? as normal condition,the football escape velocity Vmin is 21 miles per second by calculating.4) The main influencing factors of the escape velocity Vmin are air density ? and air viscosity coefficient ?. Under different temperature, air density ? and air viscosity coefficient ? also change. Through the calculation and drawing, the author found that at low temperature, escape velocity Vmin that produces the S-shaped trajectory is also low.5) The S-shaped free kick training, focused on developing the fast strength and specific skills of the lower limbs, includes the combination of different velocity centrifugal training and skillful training.