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1.
This study involved a theoretical and an experimental investigation of the direct free kick in soccer. Our aim was to develop a mathematical model of the ball's flight incorporating aerodynamic lift and drag forces to explore this important 'set-play'. Trajectories derived from the model have been compared with those obtained from detailed video analysis of experimental kicks. Representative values for the drag and lift coefficients have been obtained, together with the implied orientation of the ball's spin axis in flight. The drag coefficient varied from 0.25 to 0.30 and the lift coefficient from 0.23 to 0.29. These values, used with a simple model of a defensive wall, have enabled free kicks to be simulated under realistic conditions, typical of match-play. The results reveal how carefully attackers must engineer the dynamics of a successful kick. For a central free kick some 18.3 m (20 yards) from goal with a conventional wall, and initial speed of 25 m·s?1, the ball's initial elevation must be constrained between 16.5° and 17.5° and the ball kicked with almost perfect sidespin. 相似文献
2.
Modelling the flight of a soccer ball in a direct free kick 总被引：2，自引：0，他引：2
This study involved a theoretical and an experimental investigation of the direct free kick in soccer. Our aim was to develop a mathematical model of the ball's flight incorporating aerodynamic lift and drag forces to explore this important 'set-play'. Trajectories derived from the model have been compared with those obtained from detailed video analysis of experimental kicks. Representative values for the drag and lift coefficients have been obtained, together with the implied orientation of the ball's spin axis in flight. The drag coefficient varied from 0.25 to 0.30 and the lift coefficient from 0.23 to 0.29. These values, used with a simple model of a defensive wall, have enabled free kicks to be simulated under realistic conditions, typical of match-play. The results reveal how carefully attackers must engineer the dynamics of a successful kick. For a central free kick some 18.3 m (20 yards) from goal with a conventional wall, and initial speed of 25 m x s(-1), the ball's initial elevation must be constrained between 16.5 degrees and 17.5 degrees and the ball kicked with almost perfect sidespin. 相似文献
3.
Two different measurement techniques are used to examine the effect of surface geometry on soccer ball trajectories. Five
professional players are observed using high-speed video when taking curling free kicks with four different soccer balls.
The input conditions are measured and the average launch velocity and spin are found to be approximately 24 m/s and 106 rad/s.
It is found that the players can apply more spin (~50%) on average to one ball, which has a slightly rougher surface than
the other balls. The trajectories for the same four balls fired at various velocities and spin rates across a sports hall
using a bespoke firing device are captured using high-speed video cameras, and their drag and lift coefficients estimated.
Balls with more panels are found to experience a higher lift coefficient. The drag coefficient results show a large amount
of scatter, and it is difficult to distinguish between the balls. Using the results in a trajectory prediction programme it
is found that increasing the number of panels from 14 to 32 can significantly alter the final position of a 20 m-curling free
kick by up to 1 m. 相似文献
4.
Simon Choppin 《Sports Engineering》2013,16(3):189-194
As a bluff object, a football experiences high aerodynamic drag when flow is laminar due to early boundary layer separation and a large low-pressure region. The length and depth of a football’s seams can influence the separation point by triggering a turbulent boundary layer at lower Reynolds numbers. Football manufacturers can control a football’s behaviour through careful design and material choice. However, assessing the aerodynamic performance of a football can be a lengthy and expensive process, traditionally requiring the use of a suitable wind tunnel. Measuring the drag force at varying Reynolds numbers gives a full aerodynamic profile which determines how the ball will behave during flight. Some studies have attempted to establish the aerodynamic properties of footballs using recorded trajectories, but these only ascertained average properties rather than a full aerodynamic profile. This paper describes a method which uses a series of recorded trajectories to calculate the full aerodynamic properties of a football. To assess the accuracy and robustness of this method, simulated trajectory data were used to which varying degrees of noise and aerodynamic lift were added. The assessment found that random noise does not affect the accuracy of the methodology significantly. At larger magnitudes, random aerodynamic lift makes the methodology ineffective (equivalent to ball spin >100 rpm). Future work will concentrate on assessing the effectiveness of the methodology using ball trajectories recorded using 3D high-speed video techniques. 相似文献
5.
Chase M. Pfeifer Timothy J. Gay Jeff A. Hawks Shane M. Farritor Judith M. Burnfield 《Sports Engineering》2018,21(2):95-102
A mechanical field-goal kicking machine was used to investigate toppling ball flight in American football place-kicking, eliminating a number of uncontrollable impact variables present with a human kicker. Ball flight trajectories were recorded using a triangulation-based projectile tracking system to account for the football’s 3-dimensional position during flight as well as initial launch conditions. The football flights were described using kinematic equations relating to projectile motion including stagnant air drag and were compared to measured trajectories as well as projectile motion equations that exclude stagnant air drag. Measured football flight range deviations from the non-drag equations of projectile motion corresponded to deficits between 9 and 31%, which is described by a football toppling compound drag coefficient of 0.007 ± 0.003 kg/m. Independent variables including impact location and impact angle orientation resulted in 15 impact conditions. We found that an impact location of 5.5 cm from the bottom of the ball maximized trajectory height and distance. At the 5.5-cm impact location, alterations in impact angle produced minimal change in football trajectory, including launch angle (range = 1.96 deg), launch speed (range = 1.06 m/s), and range (range = 0.94 m). 相似文献
6.
Measurements are presented of drag and lift on new tennis balls in flight. Two video cameras were used to measure the velocity and height of the balls at two positions separated horizontally by 6.4 m. The balls were fired from a ball launcher at speeds between 15 and 30 m/s and with topspin or backspin at rates up to 2,500 rpm. Significant shot-to-shot variations were found in both the drag and lift coefficients. The average drag coefficient was 0.507 ± 0.024, independent of ball speed or spin, and lower than the value usually observed in wind tunnel experiments. The lift coefficient increased with ball spin, on average, but significant lift was observed even at very low spin. The latter effect can be attributed to a side force arising from asymmetries in the ball surface, analogous to the side force responsible for the erratic path of a knuckleball in baseball. 相似文献
7.
We assessed the net forces created when towing swimmers while gliding and kicking underwater to establish an appropriate speed for initiating underwater kicking, and the most effective gliding position and kicking technique to be applied after a turn. Sixteen experienced male swimmers of similar body shape were towed by a motorized winch and pulley system. A load cell measured net force (propulsive force - drag force) at speeds of 1.6, 1.9, 2.2, 2.5 and 3.1 m x s(-1). At each speed, the swimmers performed a prone streamline glide, a lateral streamline glide, a prone freestyle kick, a prone dolphin kick and a lateral dolphin kick. A two-way repeated-measures analysis of variance revealed significant differences between the gliding and kicking conditions at different speeds. The results demonstrated an optimal range of speeds (1.9 to 2.2 m x s(-1)) at which to begin underwater kicking to prevent energy loss from excessive active drag. No significant differences were found between the prone and lateral streamline glide positions or between the three underwater kicking techniques. Therefore, there appears to be no significant advantage in using one streamlining technique over another or in using one kicking style over another. 相似文献
8.
Vassilios Gourgoulis Alexia Boli Nikolaos Aggeloussis Panagiotis Antoniou Argyris Toubekis Georgios Mavromatis 《Journal of sports sciences》2015,33(7):696-712
The aim of this study was to assess the effect of the hand’s acceleration on the propulsive forces and the relative contribution of the drag and lift on their resultant force in the separate phases of the front crawl underwater arm stroke. Ten female swimmers swam one trial of all-out 25-m front crawl. The underwater motion of each swimmer’s right hand was recorded using four camcorders and four periscope systems. Anatomical landmarks were digitised, and the propulsive forces generated by the swimmer’s hand were estimated from the kinematic data in conjunction with hydrodynamic coefficients. When the hand’s acceleration was taken into account, the magnitude of the propulsive forces was greater, with the exception of the mean drag force during the final part of the underwater arm stroke. The mean drag force was greater than the mean lift force in the middle part, while the mean lift force was greater than the mean drag force in the final part of the underwater arm stroke. Thus, swimmers should accelerate their hands from the beginning of their backward motion, press the water with large pitch angles during the middle part and sweep with small pitch angles during the final part of their underwater arm stroke. 相似文献
9.
The effects of initial conditions on the flight of an American football kicked in an end-over-end manner were investigated using a dynamic simulation employing the quaternion method. The effects of initial tilt and spin about the longitudinal axis of the ball were considered. For the most accurate kick, our simulations show that the ball should be vertical leaving the kicker’s foot, and have no angular velocity about the longitudinal axis of the ball. A case study was performed for which experimental data were available, showing the trends of the flight of the ball captured in our simulations in actual game situations. 相似文献
10.
直接任意球在足球比赛中已经成为重要的得分手段。通过对足球任意球运行轨迹的理论分析,计算出球运行轨迹的参数,量化了直接任意球的射门在击球力量、击球部位(偏心距)、射门角度,以及球体绕过“人墙”后的最终落点。旨在当足球比赛或训练中获得距离、角度较佳的可直接射门的任意球时,针对采用直接射门如何“绕过”人墙,提供理论依据。 相似文献
11.
Kicking for distance in Australian Rules football is an important skill. Here, I examine technical aspects that contribute to achieving maximal kick distance. Twenty-eight elite players kicked for distance while being videoed at 500 Hz. Two-dimensional digitized data of nine body landmarks and the football were used to calculate kinematic parameters from kicking foot toe-off to the instant before ball contact. Longer kick distances were associated with greater foot speeds and shank angular velocities at ball contact, larger last step lengths, and greater distances from the ground when ball contact occurred. Foot speed, shank angular velocity, and ball position relative to the support foot at ball contact were included in the best regression predicting distance. A continuum of technique was evident among the kickers. At one end, kickers displayed relatively larger knee angular velocities and smaller thigh angular velocities at ball contact. At the other end, kickers produced relatively larger thigh angular velocities and smaller knee angular velocities at ball contact. To increase kicking distance, increasing foot speed and shank angular velocity at ball contact, increasing the last step length, and optimizing ball position relative to the ground and support foot are recommended. 相似文献
12.
掷界外球作为足球比赛中重新开始比赛的一种方式,与任意球、角球、点球、中圈开球等定位球相比同样是有价值的进攻得分手段。从技术动作结构分析,掌握双手投掷界外球的动作要领,克服常见的犯规,通过专项练习巩固身体肌群协调性和爆发力,改善足球掷界外球力量和距离。该文是笔者结合日常教学实践中的一些体会进行的一些理论探讨。 相似文献
13.
Kicking for distance in Australian Rules football is an important skill. Here, I examine technical aspects that contribute to achieving maximal kick distance. Twenty-eight elite players kicked for distance while being videoed at 500 Hz. Two-dimensional digitized data of nine body landmarks and the football were used to calculate kinematic parameters from kicking foot toe-off to the instant before ball contact. Longer kick distances were associated with greater foot speeds and shank angular velocities at ball contact, larger last step lengths, and greater distances from the ground when ball contact occurred. Foot speed, shank angular velocity, and ball position relative to the support foot at ball contact were included in the best regression predicting distance. A continuum of technique was evident among the kickers. At one end, kickers displayed relatively larger knee angular velocities and smaller thigh angular velocities at ball contact. At the other end, kickers produced relatively larger thigh angular velocities and smaller knee angular velocities at ball contact. To increase kicking distance, increasing foot speed and shank angular velocity at ball contact, increasing the last step length, and optimizing ball position relative to the ground and support foot are recommended. 相似文献
14.
Andrew D. Lyttle Brian A. Blanksby Bruce C. Elliott David G. Lloyd 《Journal of sports sciences》2013,31(10):801-807
Weassessed the net forces created when towing swimmers while gliding and kicking underwater to establish an appropriate speed for initiating underwater kicking, and the most effective gliding position and kicking technique to be applied after a turn. Sixteen experienced male swimmers of similar body shape were towed by a motorized winch and pulley system. A load cell measured net force (propulsive force - drag force) at speeds of 1.6, 1.9, 2.2, 2.5 and 3.1 m· s-1 . At each speed, the swimmers performed a prone streamline glide, a lateral streamline glide, a prone freestyle kick, a prone dolphin kick and a lateral dolphin kick. A two-way repeated-measures analysis of variance revealed significant differences between the gliding and kicking conditions at different speeds. The results demonstrated an optimal range of speeds (1.9 to 2.2 m· s-1 ) at which to begin underwater kicking to prevent energy loss from excessive active drag. No significant differences were found between the prone and lateral streamline glide positions or between the three underwater kicking techniques. Therefore, there appears to be no significant advantage in using one streamlining technique over another or in using one kicking style over another. 相似文献
15.
Abstract Our aim was to present a mathematical model of rowing and sculling that allowed for a comparison of oar blade designs. The relative movement between the oar blades and water during the drive phase of the stroke was modelled, and the lift and drag forces generated by this complex interaction were determined. The model was driven by the oar shaft angular velocity about the oarlock in the horizontal plane, and was shown to be valid against measured on-water mean steady-state shell velocity for both a heavyweight men's eight and a lightweight men's single scull. Measured lift and drag force coefficients previously presented by the authors were used as inputs to the model, whichs allowed for the influence of oar blade design on rowing performance to be determined. The commonly used Big Blade, which is curved, and it's flat equivalent were compared, and blade curvature was shown to generate a 1.14% improvement in mean boat velocity, or a 17.1-m lead over 1500 m. With races being won and lost by much smaller margins than this, blade curvature would appear to play a significant role in propulsion. 相似文献
16.
Stephen M. Hadlow Ross A. Pinder Mark G. L. Sayers 《Journal of sports sciences》2017,35(18):1808-1816
In Australian rules football structured increases in ball size during development end with the transition to the Size 5 (adult) ball at the Under-15 age group. This study assessed changes in kick technique and performance in experienced junior performers when using Size 4 and 5 Australian rules footballs. Participants (n = 22, 13.77 ± 0.61 years) performed drop punt kicks in 2 representative tasks; a Decision-Making Test (DMT) (n = 14) and Set-Shot Test (SST) (n = 14 + 8). Results indicate participants sustained their level of kick performance (accuracy and quality of ball spin) in both tests when using a Size 5 football. Sustained kick performance in the DMT primarily resulted from adaptations to time-point technical measures at ball release. No significant differences were detected for technical measures between ball sizes in the SST. A dynamic kicking task (DMT) in combination with ball size manipulation may have placed greater demand on skill execution in comparison to a self-paced kicking task (SST). Results provide initial support for the utility of challenging representative dynamic and self-paced tasks, such as the DMT and SST used here for Australian football, for skill testing and practice in sport 相似文献
17.
The purpose was to compare rotational and linear head accelerations as a result of taekwondo kicks and punches. Taekwondo athletes executed five repetitions of the turning kick, spinning hook kick, hook punch, straight punch, and jab punch to a Hybrid III Crash Test Dummy head-neck complex. A tri-axial accelerometer and an angular rate sensor were mounted inside the Hybrid III head to measure resultant linear (RLA) and rotational accelerations. The Hybrid III was fixed to a height-adjustable frame and fitted with protective taekwondo headgear. Dummy head height was positioned to each participant’s standing height. Acceleration data were processed in accordance with SAE J211-1.There was no significant multivariate difference in RLA but the effect was not clear. Univariate follow-up analysis showed a significant difference in RLA but the effect was also not clear. There was no difference in rotational acceleration. The highest RLA and rotational acceleration were produced, in order, by the turning kick, hook kick, hook punch, straight punch, and jab. These data are clinically important as they provide a better understanding of the biomechanical injury measures and support for improved headgear testing methodology. 相似文献
18.
Richard Mills 《Sport in History》2016,36(2):214-241
This article explores the development of a football club as a means of understanding its late adoption of professionalism and its unusual wartime conduct. Ipswich Town were the only Football League team not to kick a ball for the duration of the Second World War. Arguably, the underlying causes of the club's inactivity in both global conflicts can be found in the patriotic and staunchly amateur ethos that permeated the organisation, resulting in a very late conversion to the professional game in 1936. When the Amateur Football Association (AFA) seceded from the Football Association (FA) in 1907, Ipswich Town sided with the gentlemen amateurs and competed in the socially-exclusive Southern Amateur League until the season before the club adopted professionalism. The unique nature of Ipswich Town's evolution offers an opportunity to explore the decline of this branch of the game in the face of professional football, the protagonists who were caught up in it, and the relationship between football and civic pride. In wartime, the human and social continuities between the professional company and its amateur predecessor arguably proved to be more influential than the ruptures that resulted from a controversial inter-war abandonment of cherished amateur principles. 相似文献
19.
Jochim Spitz Koen Put Johan Wagemans A. Mark Williams 《European Journal of Sport Science》2017,17(6):748-756
Objectives: Slow-motion replays of foul play situations are now used in the education and training of sports officials. We investigated the impact of video speed on the decision-making process of association football referees and how this interacted with expertise. Methods: Three different groups of referees, varying in level of expertise, assessed video clips from an in-game perspective. Video clips represented corner kick and open play situations in which a foul occurred or not. For these foul/no foul situations, the referees had to make a technical (no foul; indirect free kick; direct free kick; or penalty kick) and a disciplinary decision (no card; yellow card; or red card), under both slow-motion and real-time viewing conditions. Accuracy scores were determined by comparing participant’s responses with the decisions of an expert panel. Results: Significant differences were observed across groups for foul/no foul situations, suggesting that the experts were able to process the available information more effectively than their less expert colleagues. The accuracy scores for the technical decision were higher in slow motion (67%) compared to a real-time viewing condition (56%), particularly for corner kick situations. No differences were found between real time and slow motion for the disciplinary decision. Conclusions: Slow-motion footage results in higher accuracy scores for complex technical decisions. These findings have implications for the use of slow-motion replays in the decision-making process of referees. 相似文献
20.
通过对第17届世界杯足球赛角球进攻战术的研究分析,发现现代足球比赛中角球进攻的新变化,如角球罚向的区域,球的运行轨迹等,以便学习世界强队在每球战术方面的长处,以利于提高中国足球水平. 相似文献