Re: How Do You Nail A Kick Shot For The Money?
- From: "Jal" <jal@xxxxxxxxxxxxxxx>
- Date: 6 Feb 2006 12:04:11 -0800
Patrick Johnson wrote:
Gregory wrote:
PJ said
* tip offset = 2/5 x distance from center to point opposite rail
contact point
Wei table diagram please.
OK.
START(
%AN7O5%BL8P7%CJ7O4%DL8N2%EM7P1%FK7P1%GK7N8%HM7N8%IL7O4%JK8M6
%KJ7P7%LJ7N2%MK7Q3%NJ7Q9%OJ7M0%Po3S3%Wo5D6%Xo1Z8%[h0D6%\s1Z5
%][8Z4%^g5C9
)END
A kick from the corner to the side. The black line through the CB shows
the centerball point. The red line shows the point on the CB opposite
the CB/rail contact point. Offset your tip to the left 2/5 (40%) of the
distance from the centerball point to the 'opposite rail contact' point.
Here is a magnified version of your diagram.
START(
%Aa0L1%B[8N1%CJ5O4%DL7N1%E\7L3%FK6P1%GK6N8%Ha7N3%I^7K0%JK6M5
%KM6O5%LJ5N2%M\7P3%NJ9Q4%OJ5M0%PB6\3%Ua2R5%Vd3V2%W^7D3%X^7R1
%Y_8Q5%Z`8P5%[W1E0%\`8P3%]O5M5%^V1D3
)END
Let the circle of balls represent the cueball. The base of the red and
blue arrows are on the surface of the cueball and both run through its
center. The green arrow is drawn perpendicular to the blue arrow to
the base of the red arrow. The contact point offset to get natural
running english (no friction) off the cushion is 2/5 of the length of
the green arrow.
However, in order to get the angle of rebound equal to the incoming
angle, I think the offset should be more like 1/5 rather than 2/5 of
this length. The cushion does not return all of the cueball's velocity
in the direction perpendicular to the cushion, but only about 0.7 - 0.8
of it. Correspondingly, the ball's velocity in the direction parallel
to the cushion also has to be slowed down.
Exactly what this offset should be depends on several factors and
assumptions. But it looks like it is roughly 1/2 of the 2/5 figure.
This may seem like a drastic reduction given that you only need to slow
it down to 0.7 or 0.8 of its parallel speed, but this depends on the
way friction acts on balls to reduce the relative surface speed between
the ball and whatever it's rubbing up against. For every unit of
surface speed taken away by a decrease in linear velocity, two and a
half units of surface speed are taken away by induced spin. So to get
the right amount of frictional braking and prevent the ball from
rolling along the cushion prematurely, you have to take away a
considerable amount from that "no friction" spin.
Some assumptions about the cushion interaction are:
1) The compression forces are distributed symmetrically about the
contact arc. (From some of Bob Jewett's data and crude observations of
my own, the indications are that this is true and that the shortening
of rebound angles is entirely or nearly entirely due to friction and
masse action.)
2) The direction of the compression forces remain about the same
throughout the impact and are pointed downward at an angle of about
15.7 degrees, depending on nose height.
3) The axis of any induced spin is tilted at this same angle away from
the vertical, and causes some masse action after the ball leaves the
cushion, shortening the rebound angle.
4) Friction with the bed as a result of the cushion pushing downward at
the above angle does produce some effects, but these are relatively
small and the cushion friction dominates.
Jim
.
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