快猫短视频

WHEN Mark McGwire earlier this week equalled baseball鈥檚 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 鈥渟weet spots鈥�.

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 快猫短视频 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鈥檚 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鈥檚 centre of percussion鈥攖he point that, if struck, will
cause the bat to recoil and rotate smoothly about an axis through the player鈥檚
wrists. The two nodes and the centre of percussion together form the bat鈥檚 three
sweet spots, Cross reports in this month鈥檚 American Journal of Physics
(vol 66, p 772).

Cross hopes that his work will help interest baseball fans in science. But he
doesn鈥檛 expect the players to spend time studying his paper. 鈥淚f I were McGwire
or Sosa, I wouldn鈥檛 worry too much about the physics.鈥�