DETERMINATION OF THE COEFFICIENT OF DRAG OF THREE DIFFERENT TENNIS BALLS USING A WIND TUNNEL

INTRODUCTION: The constant improvement of tennis rackets and coaching has changed the current game to such an extent that critics complain it is dominated by the serve. Tennis balls are being served at higher velocities with each improvement. There may soon be a point at which the receiver may not be able to react quickly enough. Before any changes can be suggested, it is necessary to have a complete understanding of the game of tennis in terms of the ball mechanics and flight. This paper documents preliminary study of the aerodynamics of tennis balls. METHODS: The investigation considered three different tennis balls, differing both in construction and quality of nap. The three ball types used are as follows: an unspoiled pressurized ball fresh from its container; an unspoiled ‘permanent’ pressure ball fresh from its container; and a well worn pressurized ball showing significant visual reduction in quality and overall bulk of nap. By using the above set of tennis balls, the effects of both construction and surface quality on a balls flight through the air were analyzed. Initial testing involved an investigation of the velocity profile of the wind tunnel. It was found that the velocity was constant across the working section up to the maximum velocity of 26ms-1. This result meant that the complete viewing area of 230mm could be used for collection of data. Three different tennis balls were dropped through the working section of the wind tunnel using an electronically activated ball drop apparatus. The wind velocity was increased in equal increments of 3ms-1, from zero to 26.3ms-1, dropping all three balls at each setting. The motion of the ball during flight was captured digitally using a KODAK Motioncorder at a frame rate of 100fs-1 and a shutter speed of 1/1000 second. The frames containing the flight of the ball were transferred from the Motioncorder and captured digitally on a computer, creating a store of several images over the duration of the flight. Data was collected from individual images using OPTIMAS 6 which exported the data to Microsoft Excel 5. The analysis used three points on the circumference of the ball, producing chords to find the its center. The resulting trajectory of the ball was viewed in the form of a graph of displacement versus time. A second order polynomial which explained the data set was fitted to the chart. The differentiation of this gave the acceleration of the ball during flight. RESULTS: The results obtained from the tests were plotted on a graph of coefficient of drag (CD) versus the Reynolds number. This chart showed that the ball with the significant removal of nap had a lower CD when compared to the balls with a brand new nap. A computational model was developed to predict the trajectory of a tennis ball. Using the results from these tests on a ball hit horizontally with an initial velocity of 26.3ms-1 and zero spin, it was estimated that the ball with the significant removal of nap would travel 1m further than the balls with unspoiled nap

How can we get more people with long-term health conditions involved in parkrun? A qualitative study evaluating parkrun’s PROVE project

Background People with long-term health conditions face barriers to physical activity and community health interventions despite potential life-changing benefits for self-management of their condition and wellbeing. A weekly mass participation running, walking and volunteering event called parkrun launched a project called PROVE in 2016 to engage people living with long-term health conditions in England. Over the 3 year project, parkrun appointed volunteer Outreach Ambassadors with a specialist interest in the health condition they represented whose role was to ensure parkrun was welcoming, supportive and inclusive. This qualitative study aimed to understand the experience of the PROVE project for people with long-term health conditions. Methods Semi-structured interviews were conducted with 15 PROVE Outreach Ambassadors representing 13 different long-term health conditions in England. Interviews were recorded, transcribed verbatim and analysed using thematic analysis. Rigour and transparency were sought in addition to utilising independent researchers to offer alternative interpretations of the data. Results Data analysis resulted in 4 overarching themes and 13 subthemes. Outreach Ambassadors believed that parkrun was already supportive of people with long-term health conditions, but that the PROVE project enabled the support to be delivered in a more structured way across health conditions and locations. Outreach Ambassadors believed that the PROVE project had the potential to create a welcoming, safe space for people with long-term health conditions to participate as walkers, runners or volunteers. Success of the PROVE project was believed to be dependent on being realistic about the potential to bring about change, challenging people’s perceptions of parkrun and engaging with key stakeholders and advocacy groups. Challenges for parkrun were believed to be around communication, demonstrating impact and the project’s dependence on volunteers for delivery. Conclusions This is the first study of its kind to explore the public health potential of parkrun for people with long-term health conditions. parkrun’s PROVE project was regarded to be important for ensuring that people with long-term health conditions can engage in physical activity and volunteering in a safe and supportive environment. The findings have important implications for parkrun, policy makers and physical activity providers looking to deliver inclusive community physical activity opportunities

The Role of Technology in Promoting Physical Activity: A Case-Study of parkrun

Around a third of people worldwide are physically inactive, causing 3.2 million deaths each year. People often use wearables and smartphone trackers to motivate them to be active, but there is evidence to show that use of these trackers declines quickly, often within weeks. One intervention that appears to successfully motivate people to be active is parkrun, a free, weekly timed 5 km run or walk every Saturday morning. The system used by parkrun is surprisingly low-tech: it uses printable barcodes, stopwatches and scanners, and the internet. A survey of 60,694 parkrun participants showed that levels of self-reported physical activity increased following participation in parkrun, especially for those with previously low levels of activity. Nine out of ten reported feeling a sense of personal achievement and improvements to fitness and physical health since starting parkrun. Based on a taxonomy of behaviour change interventions, the technology used by parkrun was shown to incorporate at least seven techniques that inform and encourage parkrunners. It is concluded that physical activity technologies should not be central to an intervention, rather, they should enhance interventions where behaviour change takes precedence

Application of serious games to sport, health and exercise

Use of interactive entertainment has been exponentially expanded since the last decade. Throughout this 10+ year evolution there has been a concern about turning entertainment properties into serious applications, a.k.a "Serious Games". In this article we present two set of Serious Game applications, an Environment Visualising game which focuses solely on applying serious games to elite Olympic sport and another set of serious games that incorporate an in house developed proprietary input system that can detect most of the human movements which focuses on applying serious games to health and exercise

Does ethnic density influence community participation in mass participation physical activity events? The case of parkrun in England

Background: parkrun has been successful in encouraging people in England to participate in their weekly 5km running and walking events. However, there is substantial heterogeneity in parkrun participation across different communities in England: after controlling for travel distances, deprived communities have significantly lower participation rates. Methods: This paper expands on previous findings by investigating disparities in parkrun participation by ethnic density. We combined geo-spatial data available through the Office for National Statistics with participation data provided by parkrun, and fitted multivariable Poisson regression models to study the effect of ethnic density on participation rates at the Lower layer Super Output Level. Results: We find that areas with higher ethnic density have lower participation rates. This effect is independent of deprivation. Conclusions: An opportunity exists for parkrun to engage with these communities and reduce potential barriers to participation

Validation of a single camera, spatio-temporal gait analysis system

such as tennis. However during competition, it is impracticable to instrument players. A markerless, view-independent, footsurface contact identification (FSCi) system was developed and validated. The FSCi system analysed standard colour video sequences of walking and running (barefoot and shod) from four unique camera perspectives; output data were compared to three-dimensional motion analysis. Results demonstrated that data for 99.6% of foot contacts (all camera perspectives) were identified. The calculation of gait variables, i.e. step length etc., was performed automatically for 91.3% of foot contact data; 8.7% of data required manual intervention for analysis. Resultant direction root-mean square error (RMSE) for foot contact position was 52.1 and 52.2 mm for barefoot and shod walking respectively. Resultant direction RMSE for foot contact position during running was 91.4 and 103.4 mm for barefoot and shod conditions respectively. The FSCi system measured basic gait parameters of walking and running without interfering with the activity being observed. The system represents a flexible approach which could be used for in situ gait analysis. The FSCi system could be used for gait analysis in competitive tennis however performance of the system when applied to larger filming areas, e.g. tennis courts, must be evaluated

Measuring the inertial properties of a tennis racket

Simple and bifilar pendulum were used to measure the mass moments of inertia of three tennis rackets. The pendulum setups were filmed using an off-the-shelf camcorder, with a stopwatch in view to provide timing data. The measurement accuracy was assessed using calibration rods of known mass moment of inertia. The simple pendulum method was found to be most accurate (<1.0 % difference to theoretical value) when a square profile rod was used as a pivot. The bifilar pendulum was found to be very accurate (0.0% difference to theoretical value) but sensitive to non-parallel support wires. A Babolat Racket Diagnostic Centre (RDC) was assessed using four calibration rods, of known mass moment of inertia. Measurement agreement was greater than 99.0% for mass moments of inertias within the range of 220 – 380 kg·cm2

A novel method to find the neutral position of the breast

Breast pain affects up to 70% of the female population. It is believed that stretching of the breast tissue causes discomfort and that by placing the breast into a position in which the tissue is neither in compression or tension (termed neutral position) will eliminate breast pain. The purpose of the study was to find a simple method that could be used to determine the location of the neutral position. One participant with a breast size of 34C performed three activities. The breast and torso movement were tracked using four retroreflective markers. The results suggest that the counter-movement jump was the most appropriate method as it forced the breast to oscillate from tension in the upper-side of the breast to tension in the under-side of the breast. The neutral position was found to be -129 ± 6 mm below the suprasternal notch, which was located 14 mm above the resting height of the breast. It was concluded that the first role of a bra is to lift the breast above the static position to cause more symmetrical oscillations about the neutral position

ASSESSING TENNIS PLAYER INTERACTIONS WITH TENNIS COURTS

Different types of tennis injury have been associated with play on different court surfaces and current knowledge of tennis player and court interactions is limited. This paper provides a brief overview of tennis injury incidence, player movements and the biomechanics of slips. The discussion proposes a new direction for assessing tennis player-surface interactions and outlines current work. It is envisaged that current work will contribute to the understanding of tennis player-surface interactions and be of practical use in the future regulation of tennis courts