RE: RE: ShopTalk: long drive

[Alan Brooks]

Since this discussion has gotten to a fairly high level, remember that 
momentum is a vector quantity that must be conserved before and after 
impact.  Since the club face is angled (loft) and the ball comes off the 
face at some launch angle, and we assume that the original velocity of the 
club head is parallel to the ground (no vertical component of momentum), 
the post-impact horizontal component of momentum of the ball plus the post 
impact horizontal component of momentum of the club head must equal the 
pre-impact horizontal momentum of the clubhead AND the vertical momentum of 
the ball and the vertical momentum of the post-impact club head must sum to 
zero (the pre-impact vertical momentum of the club head).  That is the club 
head is kicked downward with an equal momentum to the upward momentum of 
the ball.  Kinetic nergy, of course, a scalar quantity, must also be 
conserved but it is more difficult to calculate because it includes both 
the translational kinetic energy of the ball and club head and the 
rotational kinetic energy of the ball and club head.  These simple analyses 
assume both perfect collisions and no friction losses.  Real collisions are 
much more complex.

Does anybody use anything BUT Halliday and Resnick?  And I thought 
Atmospheric Physics was nothing but hot air?

Regards,
Alan Brooks

At 09:19 AM 10/14/2004 -0700, you wrote:
All:
An interesting discussion about the physics of collisions. I believe this 
is not
well understood by most people. Just a bit of my background so you know 
some of
my credentials. I am presently completely my PhD in atmospheric physics so I
hope I have at least at fundamental grasp of physics :).

First off for anyone really interested, one of the best introductory books on
physics is "Fundamentals of Physics" by Halliday and Resnick. It is a 
first year
university physics book, but I still use it for a lot of the basics. It is 
very
well written.

Concerning the transfer of speed from the clubhead to the ball...Dave T's
explanations are exactly correct. The ONLY variables in a perfect 
collision are
the clubhead velocity (for a stationary ball) and the masses of the club and
ball. Acceleration is NOT a factor. It does not matter how the clubhead has
aquired its velocity, only the magnitude of the velocity at the moment of 
impact
matters. Whether the clubhead is accelerating or decelerating is not relavent.
Someone suggested that this is not a closed system. At the moment of impact it
is a closed system. Once the ball is on its way, a further force applied 
to the
clubhead will indeed alter the clubhead's momentum. However, the ball will be
well on its way and this will have no effect on the ball speed.

Now, having said this, an interesting point was brought up. If the ball sticks
on the face for a few thousands of a second (about 5 thousanths of a sec I
believe) then continuing acceleration would be a factor. However, I 
suggest this
is so small as to be negligible.

I hope this helps a bit.
Max