shooting my age would not be a problem.
Dave Tutelman wrote:
Tedd, you're right on again, for all your points.
At 11:08 AM 10/14/04 -0400, Childers, Tedd A wrote:
What you are saying makes sense to me intuitively, but it can only affect
the impact for the very brief time of the collision (measured in thousandths
of a second probably). If the clubhead is still accelerating at the
beginning of the impact (vs. decelerating and/or constant), then it follows
that it will be traveling faster after impact. This should translate to
higher ball speed, but I'm guessing it will be a minimal increase.
Impact is very short. It is about a half a millisecond, or 1/2000 sec. Let's see just how much acceleration could affect that.
For the long-drive guy in David's test, the clubhead speed was about 150mph. Most downswings last in the vicinity of 0.3sec. So the average acceleration during the downswing would be about 500 miles per hour per second. That's average. Curves of clubhead acceleration tend to show that the acceleration is petering out by the time it gets to impact, even with a good swing. So there may be acceleration, but it will be less than the average for the downswing. Just for the sake of numbers, though, let's be generous and say 500.
Impact lasts 1/2000 of a second. So the acceleration would produce an effective speed change during impact of 500/2000 = .25. That's a QUARTER OF A MPH, out of 150. That's the maximum that acceleration could affect the clubhead speed in the momentum transfer equation. Your words were "minimal increase". I'd have to agree.
This can
be proven if we can measure the clubhead velocity immediately pre and
post-impact with the ball, as well as ball speed after impact. If higher
ball speed correlates with higher post-impact clubhead speed, you have your
answer.
The test you propose is a perfect one for experimentally choosing between the theories. You'd probably need very sensitive instruments (for instance, speeds precise to 0.1mph) in order to find a difference. You'd also need to be able to measure velocity to a time increment of a fraction of a millisecond, probably about .0001 sec. Perhaps a high-speed strobe camera: it could get the time intervals right, and could separate out clubhead and ball speed after impact. But I don't know if it would be sufficiently precise for the velocity.
You also need to be careful about assuring that the impact parameters are the same. For instance, off-center hits can make much bigger differences in ball speed than you are likely to be measuring due to acceleration.
Thanks, DaveT
