Slugging it out

日期:2017-12-05 04:57:15 作者:唐宄 阅读:

By Ian Anderson in Melbourne WHEN Mark McGwire earlier this week equalled baseball’s long-standing record of 61 home runs in a season, physics was probably the last thing on his mind. But a physicist at the University of Sydney has now worked out that the ball must have flown from a zone between 13 and 17 centimetres from the end of the bat, which contains three “sweet spots”. McGwire of the St Louis Cardinals has this season been racing Sammy Sosa of the Chicago Cubs to beat the record set in 1961 by Roger Maris of the New York Yankees. As New Scientist went to press, Sosa was trailing McGwire by three home runs. The physicist, Rod Cross, suspended a bat on a cord and used sensitive electronic devices to measure its vibration when it hit a ball. A baseball bat, much like a guitar string when it is plucked, will vibrate more at some points than at others. The spots with minimal vibration are called nodes. For a batter, these nodes are the best places at which to hit the ball. The more vibration there is, says Cross, the less energy is transferred from bat to ball and the more the batter’s hands will sting. Cross found that his baseball bat vibrated at two different frequencies, 170 hertz and 530 hertz. For each frequency, there was a node. Both were located near to the bat’s centre of percussion—the point that, if struck, will cause the bat to recoil and rotate smoothly about an axis through the player’s wrists. The two nodes and the centre of percussion together form the bat’s three sweet spots, Cross reports in this month’s American Journal of Physics (vol 66, p 772). Cross hopes that his work will help interest baseball fans in science. But he doesn’t expect the players to spend time studying his paper. “If I were McGwire or Sosa,