Sports Balls Research Articles

Calculation of the Point of Application (Centre of Pressure) of Force and Torque Imparted on a Spherical Object from Gyroscope Sensor Data, Using Sports Balls as Practical Examples.

This study investigates the determination of the centre of pressure (COP) on spherical sports objects such as cricket balls and footballs using gyroscope data from Inertial Measurement Units (IMUs). Conventional pressure sensors are not suitable for capturing the tangential forces responsible for torque generation. This research presents a novel method to calculate the COP solely from gyroscope data and avoids the complexity of isolating user-induced accelerations from IMU data. The COP is determined from the cross-product of consecutive torque vectors intersecting the surface of the sphere. Effective noise management techniques, including filtering and data interpolation, were employed to improve COP visualisation. Experiments were conducted using a smart cricket ball and a smart football. Validation tests using spin rates between 7.5 and 12 rps and torques ranging from 0.08 to 0.12 Nm confirmed consistent COP clustering around the expected positions. Further analysis extended to various spin bowling deliveries recorded using a smart cricket ball, and a curved football kick recorded using a smart football demonstrated the wide applicability of the method. The COPs of various spin bowling deliveries showed adjacent positions on the surface of the ball, traversing through backspin, sidespin and topspin, excluding the flipper and doosra deliveries. The calculation of the COP on the surface of the soccer ball could only be achieved by increasing the data sampling frequency sevenfold using curve fitting. Knowledge and use of the COP position offers significant advances in understanding and analysing ball dynamics in sports.

Early childhood physical activity parenting and sport club participation as predictors of perceived motor competence – a three-year longitudinal study

ABSTRACT Background & purpose Enhancing perceived motor competence (PMC) is an important factor in increasing the physical activity and motor competence of children. Longitudinal research is needed to identify the factors that support children’s positive and realistic PMC development. To address this research gap, we examined physical activity parenting (PAP) and sports club participation (SCP) as predictors of children’s PMC. Methods We assessed PMC using a modified pictorial scale of perceived movement skill competence (PMSC) for young children at the following two time points: in early childhood education and care (ECEC) (T1; N = 259; Mage = 6.27 ± .67; 50.2% boys) and approximately three years later in primary school (T2; N = 259; Mage = 9.45 ± .79 years). PAP and SCP (the type and number of sports) were examined using a parental questionnaire (N = 259; Mage = 36.2 ± 5.64). The children’s actual motor competence (AMC) was assessed using the Test of Gross Motor Development – Third Edition (TGMD-3). Linear regression analyses were performed to examine how the number of sports in which a child participates (SCPsum) predicted PMC. Then, we analysed how participation in a specific type of sport (locomotor and ball sports) predicted PMC in terms of locomotor skills, ball skills and total skills. The analyses were adjusted for the T2–T1 time difference and AMC. Results PAP was a significant predictor of PMC three years later for ECEC-aged girls but not for boys. Moreover, participation in a ball sport at T1 predicted higher scores for girls’ PMC at T2. In addition, the girls who participated in more than one ball sport exhibited lower PMC at T2. For boys, higher AMC, higher BMI and less access to electronic devices at T1 predicted higher PMC at T2. Conclusion The results suggest that PAP in ECEC age is important for girls’ PMC development over time. The role of SCP was ambiguous in girls. Participation especially in ball sports may have different influences on PMC in girls depending on the frequency of participation. Therefore, parents, sport instructors and coaches should adapt their child rearing and pedagogical practices by considering child PMC development in addition to promoting physical activity and skills.

THE EFFICIENCY AND COEFFICIENT OF SPORTS BALLS RESTITUTION USING AN ACOUSTIC APPLICATION

Studying the efficiency of a sports ball and its coefficient of restitution is important for performance optimization, fairness, and consistency of play. This research paper is dedicated to studying the coefficient of restitution and bounce efficiency in sports ball. Ping Pong ball and tennis balls were used to show the relationship between the bounce height and drop height. This paper used standard laboratory equipment like meter ruler, retort stand, clamp and with the utilization of the acoustic program of the smartphone using PhyPhox. The result showed that the application was able to accurately measure the bounce height in relation to the drop height. This was showed in the straight-line graph plotted. There was a constant ball efficiency coefficient of restitution and have very small percent error from the standard. This experiment can boost the interest and confidence of students in the classroom. Being able to accurately measure the performance of different balls can help students understand the science and engineering principles behind how they work. This knowledge can benefit students by allowing them to make more informed decisions when purchasing sports equipment, as well as give them an opportunity to modify their playing methods and strategies.

Playing style of women and men elite table tennis players

ABSTRACT Background: Match and notational analysis are well-recognised methods to collect important information about technical-tactical indicators in racket sports (shot, footwork, ball placement, and outcome). The purpose of this study was to analyse the principal indicators, with a special focus on comparing the playing style of women and men high-level players. Methods: twenty matches played by 40 women, and twenty matches played by 40 men were analysed in slow motion by an expert coach. All the players were in the top 111(W) and 120 (M) positions of the ITTF world ranking; Results: women play more shots/rallies and shots/games compared to men. The most used shots are Top forehand and Serve for both groups. Women also prefer to play backhand block and drive. Conversely, men prefer to counterattack with forehand Top C Top. One step is often used by women, and they also prefer to hit the ball without performing any step. Conversely, men perform crossover and pivot footwork. Serves are generally directed to close-to-the-net areas, and the following shots are typically directed to the backhand corner during the rallies. Conclusions: Women showed a specific distribution of technical indicators with respect to men players, suggesting sex-specific training sessions.

SUTTERBY NANOFLUID FLOW WITH MICROORGANISMS AROUND A CURVED EXPANDING SURFACE THROUGH A POROUS MEDIUM: THERMAL DIFFUSION AND DIFFUSION THERMO IMPACTS

This study anticipates examining a slip bioconvective movement of a non-Newtonian Sutterby nanofluid (SF) layer with motile microorganisms, where the fluid layer flows over a curved stretching surface. The movement is taken across a permeable medium under the influence of thermal diffusion, diffusion thermo, an unchanged vertical magnetic field (MF), joule heating, thermal radiation, and chemical reactions. The mathematical construction comprises momentum, energy, nanoparticles volume fraction, and microorganism concentration equations along with linear slip velocity and applicable boundary conditions (BCs). The motivation of the problem concerns recent progress in curved electronics and microchip technology, which made a growing development of the remarkable weaknesses of traditional planar electronics, which concerns the importance of the current work. Furthermore, the implication of this work emerges from the participation of microorganisms in the flow over a curved surface and shares with the temperature, velocity, and nanoparticle system of equations. This prototype is widely applicable in some manufacturing and engineering mechanisms like conduits, sports balls, combustion, inflated broadcast, and flow-structure contact between hydrodynamics and aerodynamics. The configuration of nonlinear partial differential equations (PDEs) is converted into ordinary differential equations (ODEs) by consuming suitable similarity transformations. The resulting equations are numerically analyzed via the fourth-order Runge-Kutta (RK-4) in concurrence with the shooting technique. The graphical construction of the targeted distributions is analyzed to recognize the effects of the relevant material coefficients. As key outcomes, it is noted that the greater the curvature of the surface, the greater the temperature, velocity, microorganisms, and nanoparticle distributions. Correspondingly, the Soret and Dufour impacts are found to be the improvement coefficients of the heat and dampness of both nanoparticle and microorganism condensation. Additionally, heat transmission develops with almost all relevant parameters, which is a noteworthy finding that can benefit potential applications.

Effects of adding dual-task or sport-specific task constrains to jump-landing tests on biomechanical parameters related to injury risk factors in team sports: a systematic review.

Jumping and landing tests are frequently used as a tool to assess muscle function. However, they are performed in a controlled and predictable environment. The physical tests commonly used as part of the criteria for return to sport after injury are often performed with little or no cognitive load and low coordinative demand compared to game-specific actions. The aim of this systematic review was to examine the influence of performing a dual task (DT) or sport-specific task constrains during jump-landing tests on biomechanical variables related to lower limb injury risk in team sports. This systematic review followed the specific methodological guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The search was conducted in the databases Medline (PubMed), Web of Science, Cochrane Plus, and SportDiscus for studies published from 2013 until June 30, 2023. To be eligible, studies had to include: (1) kinematic and/or kinetic assessment of injury risk factors in the lower extremity; (2) a comparison between a simple jump or landing test and a DT jump or landing test which included cognitive information. The risk of bias in the selected articles was analyzed using the recommendations of the Cochrane Collaboration. Of the 656 records identified, 13 met the established criteria. Additionally, two more articles were manually included after screening references from the included articles and previous related systematic reviews. Regarding the Risk of bias assessment, 12 studies did not surpass a score of 3 points (out of a total of 7). Only three studies exceeded a score of 3 points, with one article achieving a total score of 6. From the included studies, comparative conditions included actions influenced by the inclusion of a sports ball (n=6), performing tasks in virtual environments or with virtual feedback (n=2), participation in cognitive tasks (n=6), and tasks involving dual processes (n=7). The execution of decision-making (DM) during the jump-landing action resulted in biomechanical changes such as lower peak angles of hip flexion and knee flexion, along with increased vertical ground reaction force, knee abduction, and tibial internal rotation. Regarding limitations, discrepancies arise in defining what constitutes DT. As a result, it is possible that not all studies included in this review fit all conceptual definitions of DT. The inclusion of DT or constraints in jump-landing tests significantly alters biomechanical variables related to lower extremity injury risk in team sports. In future research, it would be beneficial to incorporate tasks into jumping tests that simulate the specific cognitive demands of team sports. This systematic review was registered in PROSPERO (registration number: CRD42023462102) and this research received no external funding.

On exact wave propagation analysis in a beach volleyball ball

Wave propagation and vibration state in the sports balls have important effects on the stability in movement and accuracy of hits. In some sports, similar to football and volleyball, the balls are subjected to continuous strong hits from players. In the current study, the wave propagation in a beach volleyball ball under the effect of temperature change, different material characteristics, different thicknesses, and the total mass is investigated. In this regard, the ball is modeled using a spherical shell structure and a higher-order displacement field is considered. The classical theory of elasticity is employed along with Hamilton’s principle for the spherical shell. The outcome equations with different boundary conditions are solved by engaging the discrete singular convolution method (DSCM). In addition, the finite element method is used to obtain the modal shape and natural frequency. The formulations and solution method are utilized in different steps of convergence examination, validation, and parametric study to acquire a comprehensive insight into the behavior of beach volleyball balls under the effect of the dynamic loading conditions. In specific, we are more interested in the phase velocity of the ball. The results are presented for different temperature changes and geometrical and material properties.

Aerodynamics of Sport Balls, Badminton Shuttlecock and Javelin

The focus of the present chapter is to analysis aerodynamic forces and moment on sport balls, badminton shuttlecock and javelin. Lift force is analytically obtained employing Kutta-Joukowski theorem over a spinning sphere in an inviscid and incompressible flow. The inviscid flow analysis reveals that lift force is directly proportional to spinning which coincides with the experimental data of Bearman and Harvey. The lift force over the spinning sphere is less as compared to a rotating cylinder. The tangential velocity component on the surface of the spinning sphere is a cubic algebraic equation which has one real and two conjugate imaginary roots. Aerodynamic performance of feather and synthetic badminton shuttlecock is discussed in conjunction with experimental data. Available video images of a javelin trajectory are used to reconstruct its aerodynamic performance.

15 Getting Over Ourselves

15 Getting Over Ourselves Mimi Thi Nguyen (bio) I enrolled in my first ethnic studies course as an undergraduate in 1993, and it was, to put it mildly, disappointing. Punk had given me my first radical education in US empire, the police state, and the riot, and gender and women's studies my second radical education in postcolonial and women of color feminisms. But what I remember most about that first ethnic studies course was the professor telling crude jokes about balls (specifically the correspondences between the relative heft of sports balls and testicles) and holding court about his arrests some thirty years ago, and that halfway through the semester I began skipping both the lecture and discussion sections except for exams. For a young woman of color feminist who understood herself as an activist, and had also become interested in what theory could diagnose about the failures of movements, the course was a wash. Even at twenty years old, I knew something about the obstacles of radical self-aggrandization. Even as I write this now, a white lesbian "superstar" intellectual stands accused of abuses of power made possible by her entrenched position within a structure and an enterprise, and her supporters twist themselves to justify these abuses through appeals to the radicalism of their own intellectual labor.1 As a number of us have said to each other throughout this latest debacle, everything is terrible. Here, then, is where I want to begin: where radicalism (an uneasy referent, as any student of social movements—or a predatory professor—knows), race, and the institutions of knowledge elaborate each other as objects of profound investment for both political capital and capital accumulation. What can we make of the machinations that anoint the radical intellectual as foundation and arbiter of radical knowledge, which is both the premise of their claims to "outsider" [End Page 343] status to the institution, but also to those goods that the institution provides to some and not others, including healthcare, tenure, and a paycheck? And how do we as scholars of power, in both senses as critics and as agents, narrate the crises we purport to resolve? There are questions I learned to ask and begin to answer through the interdisciplines that are my intellectual genealogies, including gender and women's studies and ethnic studies; these same interdisciplines that are my institutional "homes" reproduced and even amplified some of these conditions. So here I rehearse two modest proposals. First, we must account for the material conditions that support—or not—our labor. Second, our scholarship need not (and sometimes cannot) be commensurate with an identifiable activist project or form of resistance to be "properly" political. To put it another way: How does the valorization of certain intellectual labors foreclose possibilities for future collectivities, and necessary accounts of power? I For those of us in or from interdisciplines such as ethnic studies and gender and women's studies, our institutional histories as fields of inquiry and administrative academic units are often related (though in no straightforward manner, despite the conventional story) as histories of student upheavals and popular demands. From these histories arises the fiction that produces "the people" as an object of knowledge that claims and hails the radical intellectual as their interlocutor, translator, arbiter, or representative otherwise within the institution. This relation between "the people," "the community," and the old-fashioned "masses," and the radical intellectual has long been the occasion for reflecting upon the affinities and fault lines between forms (and categories) of movement work. In a still-crucial essay—one I read as an undergraduate, and which likely informed my bad attitude in that ethnic studies course—Trinh T. Minh-ha troubles the theoretical formation of "the masses" and the author or artist as their avatar, writing, "One invokes them and pretends to write on their behalf when one wishes to give weight to one's undertaking or to justify it."2 Or as Nick Mitchell observes in his schematic history of the "(critical ethnic studies) intellectual," the presumptive inseparability of representation in knowledge and representative in politics valorizes the intellectual as a figure of fantastical investment, especially for the intellectual herself.3 Both...

Sports ball projectile ocular trauma in dogs

To describe the clinical features, management, and outcome of dogs presenting with sports ball projectile ocular injuries. Eighteen dogs. A retrospective study reviewing cases of ocular injury due to a sports ball projectile that presented to the Cornell University ophthalmology service between 2004 and 2021. Dog age, type of sports ball, initial ocular lesions, eye affected, clinical management, and visual outcome were recorded. Sports ball projectile ocular injuries were identified in 18 eyes of 18 dogs. The median age of the dogs was 1.0 years old, ranging from 0.3- to 9-years- old. Nine dogs were male, and 9 were female. Ocular injuries were caused by small, dense balls (e.g., golf balls, baseballs) in 11 dogs; small, light balls (e.g., tennis balls, toy balls) in 5 dogs; and large, soft balls (e.g., soccer ball, football) in 2 dogs. Closed-globe injuries (12 of 18 eyes) presented with traumatic uveitis (91%), hyphema (45%), and subconjunctival hemorrhage (18%). All 12 closed-globe injury cases were medically managed, eight dogs remained visual. Open-globe injuries (6 of 18 dogs) presented with three corneal lacerations and three scleral ruptures. Five open-globe injuries required enucleation, and one was medically managed and maintained vision. Sports ball projectile ocular injuries in dogs can result in substantial ocular morbidity and in loss of vision. Small, dense balls were associated with injuries that carried the most guarded prognosis and required more aggressive management. Small and large lighter projectiles were associated with less serious ocular injuries and visual outcomes.

Inelastic bouncing of a spherical ball in the presence of quadratic drag with application to sports balls

The bouncing motion of a spherical ball following its repeated inelastic impacts with a horizontal flat surface is analyzed. The effect of air resistance on the motion of the ball is accounted for by using the quadratic drag model. The effects of inelastic impacts are accounted for by using the coefficient of restitution, which is assumed to remain constant during repeated impacts. Also presented is an extension of the analysis allowing for a velocity-dependent coefficient of restitution. Closed-form expressions are derived for the velocity, position, maximum height, duration, and dissipated energy during each cycle of motion. The decrease of successive rebound heights in the presence of air resistance is more rapid for higher values of the launch velocity, because the drag force is stronger and acts longer. Air resistance can significantly affect the value of the coefficient of restitution determined in a dropping ball test. For a given number of rebounds, the energy dissipated by inelastic impacts is greater than the energy dissipated by air resistance, if the launch velocity is sufficiently small. The opposite is true for greater values of the launch velocity. The derived formulas are applied to analyze the bouncing motion of a ping pong ball, tennis ball, handball, and a basketball.

Comparison of the Impulse the New BETA Volleyball Designed With Other Volleyballs Samples

Background and aim The sport of volleyball requires constant contact of sports balls with the hands of athletes, Therefore, the sports balls used in volleyball can play an important role in the performance of athletes. therefore, the aim of the present study is to compare the impulse of the new BETA volleyball designed with other samples volleyballs using the Bertak model force plate made in the United States. Material and Methods Examples of Mikasa volleyballs, model V200W, made in Japan, Fox volleyball, model Spain, made in France and Old and new BETA volleyballs made in Iran with a weight range of 260 to 270 grams with a circumference of 66 cm were used in the present study, Finally, the impulses of volleyballs were compared using a Bertek model force plate machine. Results In line with the findings of the present study, there is a significant difference between the impulse of the sample of the new BETA volleyball ball designed at compared to the volleyball sample of the old beta design in the direction of the vertical axis (P = 0.014). in this regard, the post hoc test showed that there is no statistically significant difference between the sample of the new BETA volleyball at compared to the sample of Fox volleyball (P = 0.102) and Mikasa volleyball that is used in official competitions (P = 0.662). Conclusion Therefore, the use of a new BETA volleyball designed to reduce the rate of sports injuries is recommended to all coaches, referees, athletes and officials in the field of volleyball.

Baseball Drag Measurements in Free Flight

While baseball is a popular sport with a storied history, the aerodynamic properties of the seamed sports ball are not fully understood. Reported aerodynamic baseball behaviors are primarily based on force measurements from wind tunnels. The following describes a methodology to measure baseball drag in free flight from changes in its speed. The method relies on a high accuracy ball delivery device and speed measurement system. It avoids the large infrastructure, stinger attachment and blockage effects associated with wind tunnels. In the present work, we examined the baseball drag as a function of orientation and with spin. The drag values retrieved from the proposed method are in good agreement with radar and video measurements. However, they are lower than those reported in other wind tunnel measurements, which was attributed to differences in the balls that were tested or the stinger attachment.

Enhancement of Speed and Accuracy Trade-Off for Sports Ball Detection in Videos-Finding Fast Moving, Small Objects in Real Time.

The detection and localization of the ball in sport videos is crucial to better understand events and actions occurring in those sports. Despite recent advances in the field of object detection, the automatic detection of balls remains a challenging task due to the unsteady nature of balls in images. In this paper, we address the detection of small, fast-moving balls in sport video data and introduce a real-time ball detection approach based on the YOLOv3 object detection model. We apply specific adjustments to the network architecture and training process in order to enhance the detection accuracy and speed: We facilitate an efficient integration of motion information, avoiding a complex modification of the network architecture. Furthermore, we present a customized detection approach that is designed to primarily focus on the detection of small objects. We integrate domain-specific knowledge to adapt image pre-processing and a data augmentation strategy that takes advantage of the special features of balls in images in order to improve the generalization ability of the detection network. We demonstrate that the general trade-off between detection speed and accuracy of the YOLOv3 model can be enhanced in consideration of domain-specific prior knowledge.

Drag coefficients of air rifle pellets with wide range of geometries

Air rifle and air pistol target shooting are included in major intentional and national sports competitions and are also highly popular sport pastimes. Published scientific studies of pellet drag are very rare, in contrast to a large number of scientific studies published on aerodynamic drag of sports balls and other sports projectiles. Measurements are presented of the drag coefficients for 31 air rifle pellets of mainly 4.5 mm (0.177 in) calibre having a wide range of geometries. The drag coefficient measurements were made with a low-turbulence open wind tunnel at flow velocity of 200 m/s (Mach and Reynolds numbers 0.57 and 56,000 for 4.5 mm pellets). The detailed geometry of some pellets was altered systematically in order to improve understanding of how pellet geometry affects drag coefficient. The drag coefficient for the 31 pellets varied widely from 0.36 to 0.78, and it was influenced substantially by the curvature of the flow separating from the pellet head rim. Large curvatures delayed flow re-attachment onto the pellet tail, thereby lowering pellet base pressure and increasing the value of drag coefficient. Pellets with hemi-spherical or ogive-shaped noses generally had lower values of drag coefficient than pellets with other nose shapes. The presence of the pellet tail was beneficial by providing a surface onto which the flow detaching from the pellet rim could re-attach. However, for minimisation of drag coefficient, the pellet tail had to be of a certain optimum length which depended on the shape of the pellet nose. Small differences in pellet geometry had significant influence on the value of drag coefficient. Increase in air velocity from 120 to 200 m/s had small influence on the value of drag coefficient for three common sports pellets having flat, conical and dome-shaped noses.

The Role of Boundary Layer Theory in Soccer Ball Dynamics

The boundary layer theory plays a major role in the development of fluid mechanics applications especially in the sports ball dynamics. Whenever an object travels through the air, it experiences aerodynamic forces acting on it. Sport balls, uses these forces to deviate from its expected path of flight. Thus, creating an advantage which can be exploited by the playing members to improve their skills. The present study focuses on numerical simulation of aerodynamic flow over a soccer ball and estimated the drag coefficient. In order to a get more precise results, the effect of gravity is included to study the dynamics of flow. The variation of drag coefficient is plotted as a function of Reynolds number and wind speed. The computational result had a good agreement with existing empirical data.

Exploring human-nature interactions in national parks with social media photographs and computer vision.

Understanding the activities and preferences of visitors is crucial for managing protected areas and planning conservation strategies. Conservation culturomics promotes the use of user-generated online content in conservation science. Geotagged social media content is a unique source of in situ information on human presence and activities in nature. Photographs posted on social media platforms are a promising source of information, but analyzing large volumes of photographs manually remains laborious. We examined the application of state-of-the-art computer-vision methods to studying human-nature interactions. We used semantic clustering, scene classification, and object detection to automatically analyze photographs taken in Finnish national parks by domestic and international visitors. Our results showed that human-nature interactions can be extracted from user-generated photographs with computer vision. The different methods complemented each other by revealing broad visual themes related to level of the data set, landscape photogeneity, and human activities. Geotagged photographs revealed distinct regional profiles for national parks (e.g., preferences in landscapes and activities), which are potentially useful in park management. Photographic content differed between domestic and international visitors, which indicates differences in activities and preferences. Information extracted automatically from photographs can help identify preferences among diverse visitor groups, which can be used to create profiles of national parks for conservation marketing and to support conservation strategies that rely on public acceptance. The application of computer-vision methods to automatic content analysis of photographs should be explored further in conservation culturomics, particularly in combination with rich metadata available on social media platforms.

Flight and bounce of spinning sports balls

Standard university or high-school physics teaching material on projectile motion is usually based on Newton's second law in vacuum, neglecting aerodynamics. We present a low-cost experiment for teaching projectile motion using the students' cell phones and sports equipment, which allows the students to test theory and numerical simulation against experimental data in the real world. For a shot put, theoretical predictions assuming projectile motion in vacuum agree with experimentally obtained trajectories in air to within a few centimeters. However, for a table tennis ball, vacuum trajectories can be almost three times as long as experimentally obtained trajectories. An equation of motion including the aerodynamic drag force has no analytic solution, but it is straightforward to integrate numerically for high-school or first-year university students. Accounting for aerodynamic drag substantially improves the match with experimental data for any ball. In a second experiment, balls are shot with spin resulting in curveball trajectories. Numerical simulations including the Magnus force can give accurate predictions of 3D curveball trajectories, both curving according to the normal and the inverse Magnus effect. Balls shot with topspin and backspin are also accurately modelled. Finally, we model the bounce of an arbitrarily spinning ball using linear and angular impulse-momentum theorems and coefficients of restitution in vertical and horizontal directions. We find agreement with experimental data to within centimeters.

Sports balls as potential SARS-CoV-2 transmission vectors

Objects passed from one player to another have not been assessed for their ability to transmit severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We found that the surface of sport balls, notably a football, tennis ball, golf ball, and cricket ball could not harbour inactivated virus when it was swabbed onto the surface, even for 30 ​s. However, when high concentrations of 5000 ​dC/mL and 10,000 ​dC/mL are directly pipetted onto the balls, it could be detected after for short time periods. Sports objects can only harbour inactivated SARS-CoV-2 under specific, directly transferred conditions, but wiping with a dry tissue or moist ‘baby wipe’ or dropping and rolling the balls removes all detectable viral traces. This has helpful implications to sporting events.

The Exponent of the Dependence of Impact Force on Impact Velocity

Injury may result if the head is struck by a projectile (e.g., a nonlethal weapon or a sports ball), even if the projectile is of small mass and has a soft exterior. Some theory is available concerning the dependence of maximum force on the impact velocity and mass of the projectile. In light of that, comments are made on recently published data.