Aerodynamics of Sports Balls

Mehta, R.

doi:10.1146/annurev.fluid.17.1.151

Cited by 43 publications

(62 citation statements)

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“…where dd/dt is the rate of change of relative disparity for an object at a straight-ahead location that is approaching the observer at speed V along a line that passes midway between the eyes. In principle, sensitivity to dd/dt can extend to further distances than static stereopsis, because speed is pitted against D 2 in Equation 8. From Equations 4 and 8 we have…”

Section: Ttc ¼ H=ðdh=dtþ ð 4þmentioning

confidence: 99%

“…The complex aerodynamics that undrlies this kind of 'swing' bowling has been analysed both mathematically, and experimentally including the use of wind tunnels. [5][6][7][8][9][10] The title of a book written by a captain of the England team is telling: 'I Don't Bruise Easily'. 11 As demonstrated by McCabe in 1932, an effective response to such intimidation is the hook stroke illustrated in Figure 1.…”

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confidence: 99%

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Vision and cricket

Regan

2012

Ophthalmic Physiologic Optic

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This review discusses the hypothesis that hitting a cricket ball depends on predicting the instant that the ball will be located in the volume of space within which it can be successfully hit, and that this prediction is based on retinal image correlates of the direction of motion in depth and the time to collision (or time to passage). The performance of top cricket players allows an estimation of their accuracy in this spatio-temporal prediction. The bowler challenges the batsman's skill by (1) causing the ball to change direction in flight and/or after bouncing and (2) causing linked variations in the speed and trajectory of the ball. I suggest that the linked variations of speed and trajectory exploit a visual inadequacy of the batsman, namely poor sensitivity to the instantaneous absolute distance and speed of the ball. Two alternative hypothese are also discussed, one based on eye movements, the other based on continuous coupling between perception and action.

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Section: Ttc ¼ H=ðdh=dtþ ð 4þmentioning

confidence: 99%

mentioning

confidence: 99%

Vision and cricket

Regan

2012

Ophthalmic Physiologic Optic

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“…The lateral deflection of a spinning ball in flight used by many famous footballers like David Beckham during a free kick is generally known as the ''Magnus effect'' named after the German physicist Gustav Magnus who investigated the deflection of spinning cylinders in the mid-19th century. The two components of the total aerodynamic force that act on a spinning soccer ball flying through the air are the drag force which slows the ball down and the lift or side force which makes the ball dip or curve (Mehta, 1985). The drag force acts along the direction of motion whereas the lift force acts in a direction normal to it.…”

Section: Physical Effects Of High Altitude ''Bend It Like Beckham'' (mentioning

confidence: 99%

Effect of altitude on football performance

Levine

Stray-Gundersen

Mehta

2008

Scandinavian Med Sci Sports

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Altitude will impact football performance through two separate and parallel pathways related to the hypobaric (physical) and hypoxic (physiological) components of terrestrial altitude: (a) the decrease in partial pressure of oxygen reduces maximal oxygen uptake and impairs "aerobic" performance by reducing maximal aerobic power, increasing the relative intensity of any given absolute level of work, and delaying recovery of high-energy phosphates between high-intensity "interval" type efforts; (b) the decrease in air density reduces air resistance which will facilitate high-velocity running, but will also alter drag and lift thereby impairing sensorimotor skills. These effects appear to have their greatest impact very early in the altitude exposure, and their physiological/neurosensory consequences are ameliorated by acclimatization, though the extent of restoration of sea level type performance depends on the absolute magnitude of the competing and living altitudes.

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“…Haake et al between 0.075 and 0.275 for C L , depending upon the ratio of linear to rotational velocity. The drag and lift force F D and F L for a spinning object are characterised by the following formulae (Mehta 1985):…”

Section: Introductionmentioning

confidence: 99%

Engineering tennis - slowing the game down

et al. 2000

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Analysis of results from the four major tennis tournaments shows that the percentage of tie breaks in the men’s game has been increasing over the last 30 years. It is hypothesised that this is due to the increasing speed of the serve in the game. There was found to be a significant difference in tie breaks between slower clay surfaces and faster grass surfaces. The women’s game, on the other hand, showed no increase in tie‐breaks and no difference in the number of tie‐breaks between court surfaces. A larger tennis ball was assessed to see its effect in slowing the game down. Standard and 6% larger pressurised tennis balls were used in experiments to study impacts with a fixed and a freely suspended tennis racket. The coefficient of restitution of the larger ball was found to be larger in the fixed racket tests and analysis of a serve showed that the larger ball would be served marginally faster than a standard sized ball. Drag forces on tennis balls in flight were analysed by mounting tennis balls in a wind tunnel at wind speeds up to 66.6 ms−1 (150 mph). It was found that different brands of standard size tennis ball and a larger tennis ball had a drag coefficient of approximately 0.55. Raising or reducing the nap of the ball changed the drag coefficient by about 10%. Impact experiments of tennis balls on court surfaces showed that the larger and standard tennis balls rebounded at approximately the same speed at 70% of impact speed on acrylic and 64% of impact speed on clay. Both sizes of ball bounced steeper off clay than on acrylic. It appeared that the larger ball rebounded steeper than the standard ball, although evidence for this was clouded by considerable scatter in the data. A computer trajectory program was used to analyse simulated first and second serves at nominally 53.3 ms−1 (120 mph) and 40 ms−1 (90 mph). It was found that a larger ball would increase travel time to the baseline by approximately 10 ms for a first serve and up to 16 ms for a second serve. This increase was found to be just less than half that between acrylic and clay for the same ball. Travel time is increased further if the ball is increased in diameter. It was concluded therefore that the introduction of a larger ball could slow the game of tennis for all strokes and increase the time available for the receiver to return the ball.

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Aerodynamics of Sports Balls

Cited by 43 publications

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Vision and cricket

Vision and cricket

Effect of altitude on football performance

Engineering tennis - slowing the game down

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