Biomedical subjects

Rod Cross

Publications and source records attributed to Rod Cross.

3 recordsLinked to original sources

PubMed2006

Effects of swing-weight on swing speed and racket power.

Measurements are presented of the speed at which six different rods could be swung by four male students. Three of the rods had the same mass but their swing-weight (i.e. moment of inertia) differed by large factors. The other three rods had the same swing-weight but different masses. Our primary objective was to quantify the effects of mass and swing-weight on swing speed. The result has a direct bearing on whether baseball, tennis, cricket and golf participants should choose a heavy or light implement to impart maximum speed to a ball. When swinging with maximum effort, swing speed (V) was found to decrease as swing-weight (Io) increased, according to the relation V = C/Ion, where C is a different constant for each participant and n = 0.27 when Io > 0.03 kg x m2. Remarkably similar results were obtained previously with softball bats (where n = 0.25) and golf clubs (where n = 0.26). Swing speed remained approximately constant as swing mass increased (when keeping swing-weight fixed). The implications for racket power are discussed.

Acceleration↗

PubMed2006

Fatal falls from a height: two case studies.

Two case studies are presented involving fatal falls of adult females from a height. One involved a launch at low speed from a balcony, and one involved a launch at high speed from the top of a cliff. Crime scene evidence obtained on the balcony itself provided a strong indication of homicide, but subsequent investigation showed that the fall was accidental. No crime scene evidence was obtained for the cliff fall since the fall initially appeared to be just another suicide from a popular suicide spot. Subsequent investigations indicated homicide based on measurements of cliff height, horizontal distance to the impact, and available runup distance, plus measurements of possible run, jump, and throw speeds. It was found that a female weighing 61 kg (134 lb) can be thrown at speeds up to 4.85 m/s by a strong male, more than enough to account for the estimated launch speed (4.5 m/s). Given the available 4.0 m runup distance, it was found that women of better than average rather than elite athletic ability can dive at speeds of about 3.5 m/s or jump feet first at speeds of about 4.0 m/s, both being less than the estimated launch speed. The decedent had no athletic ability and landed head first after falling through a height of 29 m.

Accidental Falls↗

PubMed2005

String tension effects on tennis ball rebound speed and accuracy during playing conditions.

The primary aim of this study was to determine whether variations in rebound speed and accuracy of a tennis ball could be detected during game-simulated conditions when using three rackets strung with three string tensions. Tennis balls were projected from a ball machine towards participants who attempted to stroke the ball cross-court into the opposing singles court. The rebound speed of each impact was measured using a radar gun located behind the baseline of the court. An observer also recorded the number of balls landing in, long, wide and in the net. It was found that rebound speeds for males (110.1+/-10.2 km.h-1; mean+/-s) were slightly higher than those of females (103.6+/-8.6 km.h-1; P<0.05) and that low string tensions (180 N) produced greater rebound speeds (108.1+/-9.9 km.h-1) than high string tensions (280 N, 105.3+/-9.6 km.h-1; P<0.05). This finding is in line with laboratory results and theoretical predictions of other researchers. With respect to accuracy, the type of error made was significantly influenced by the string tension (P<0.05). This was particularly evident when considering whether the ball travelled long or landed in the net. High string tension was more likely to result in a net error, whereas low string tension was more likely to result in the ball travelling long. It was concluded that both gender and the string tension influence the speed and accuracy of the tennis ball.

Adult↗