Ristometer to measure green friction
In
the "weightlessness" and "vacuum"
of space, a putt will impart to a golf ball a force
of acceleration that will change the ball's state
from one of rest to one of constant velocity, and
the velocity will stay the same thereafter until the
Crack of Doom (unless the ball is affected by some
other force). On the earth, there is always "some
other force" hanging around: gravity. That's
why a canon ball fired at 45 degrees inclination from
the surface makes a parabolic rainbow trajectory as
gravity pulls it back to earth. Gravity is not sudden
or variable, but is always steady. That's why the
parabola shape of the canon ball is smooth and predictable.
That's very helpful in putting, since gravity is very
predictable and putt paths never have kinks or angles
in them.
But
a putted ball never goes up into the air like a canon
ball, so how can gravity affect it? If you place a
ball on a flat and level marble table that extends
for a mile and then putt the ball, the ball will roll
straight but it will eventually slow down and stop.
Why? Because of friction between the bottom of the
ball and the table (and a little air resistance) --
in this case, not much at all, but some. The steady
influence of this friction eventually wears down the
forward motion of the ball. Now imagine the same marble
table in space. The putt will roll straight on the
table surface but will never stop. The lesson is that
gravity is what makes friction.
The
other lesson is that the surface also makes friction,
or more correctly, the contact between the ball and
the surface. (That's why tire treads have best contact
with the road when they are not fully inflated.) So,
in putting, since neither the ball nor gravity ever
changes, the only thing that affects the extent of
friction is the surface. Tightly mown, tournament-condition
bent grass has little friction compared to shaggy,
late-in-the-day bermuda. Wet grass is slower than
dry grass, because it has less friction.
And,
although it is a minor point, it is not really accurate
to say that gravity is never different for a given
putt, although gravity itself never changes. That's
because it does matter in any given putt what sort
of tilted surface the ball has to cross. For friction,
not all gravity matters, and only that component of
gravity that is directed flush into the surface creates
the friction. So a ball rolling across a flat and
level putting mat has Friction=2 but when you tilt
the matt on its side and roll the ball across it,
then the Friction=1 (less). Only some of the gravity
is holding the ball against the surface in the second
case. So, sidehill breaking putts can actually involve
less friction than putts across an untilted surface
and putts downhill have a little less friction, too
(not much). Putts uphill have a little more friction,
not from the tilt's reducing the component of gravity,
but from the forward motion of the ball running it
into the surface harder.
Grain
in a green is an "opposing force" when the
ball is rolling into the grain because the angled
tips of the grass blades act like miniature pikes
defending against the onslaught of the ball, and grain
is very similar to friction, but only when the ball
is going "into the grain." Like tilt, grain
has its maximum effect only when the ball is going
directly into the grain, and when the ball rolls athwart
the grain or with the grain, there is less to none
opposing force. (It's not really correct to think
of grain as making putts slower OR FASTER, since grain
only works to slow the ball's roll, and never really
speeds it up. When the ball rolls with the grain,
there is simply less opposing force, and there may
even be less friction too, so that the same putt across
a level no-grain surface rolls at Speed=1 whereas
the same putt across a level with-the-grain surface
will roll faster, at Speed=2.)
So
Touch necessarily involves an appreciation for gravity's
effect on a ball in general, how gravity creates friction
between the ball and the green, and how this friction
can be greater or lesser depending upon the contour
and condition of the green (including grain).
Green
Speed Factors
The
main factors in green speed are type of grass and
grass condition. Bent grass that has been recently
mowed to under 1/8th an inch and rolled will be a
lot faster (less friction) than day-old bermuda that
has seen 50 foursomes tromping through. The other
factors are relatively insignificant compared to these
basics. Other
factors include moisture, surface irregularities (footprints,
debris, spike marks, ball pitch marks), maintenance
and preparation practices, and invasive weeds or disease
patches.
Mositure
is not simply dew or rain or recent sprinkling for
irrigation: it also includes the water content of
the grass blades and turf as well as the humidity
of the air. Sometimes winter greens can be very fast
because the growth of the grass is curtailed and the
air is dry (although frigid). These greens are faster
than the same grass height on a hot humid summer day
in the South. The humidity tends to prevent the water
content of the grass blades from evaporating, so the
leaves have more of a lush character that retards
the roll of the ball more. So watch out on a day when
the air is dry, the temperature high, and the wind
on the fly -- the green will get blow-dried to a crisp
and be faster than a cat on fire. By the same token,
watch out for greens where half the green is in the
shade of a tree -- the shade will keep the grass cool
and moist and will be a little slower than the sunny
part of the green. And, by the same reasoning, greens
that sheltered down in the terrain are apt to be slower
than greens perched on a hilltop exposed to the wind.
And, same thing, greens that are down low in the surrounding
terrain in the pathway of the drainage of higher terrain
will be slower than greens on an elevation in the
local terrain, with no "upstream" drainage
coming its way.
You
can often tell mositure content of a green from looking
at its color (moist makes it darker), from the sponginess
of the turf under your feet, and from taking a peek
into the hole at the exposed turf to see if it looks
moist or dry. (PGA Tour greens have this exposed turf
covered up with white paint for television.) A greenkeepr
has a tool made from a iron with the shaft cut off
near the head, and he sticks the hollow shaft into
the green 3 to 6 inches and removes a sample plug
to inspect by sight, taste, smell or feel for its
moisture content. The golfer can use sight, feel of
the feet (not the hands), and smell, without violating
the Rule against "testing" the surface.
Greens
are typically watered overnight and then perhaps again
at the start of the day, so morning greens have the
most moisture on a rainless day. As the sun warms
up, the greens dry out and get faster. Later in the
day, as the grass grows, there is a mixture of influences
-- some slowing the green (growth, humdity, and rain)
and some speeding it up (dry air, heat, sunlight,
wind). The change in green speed from recently mown
morning greens to dried mid-morning / early afternoon
greens to cool and humid early evening greens can
be very considerable. It is always a good idea to
listen to the green speed through your feet. At Augusta
in the 1950s and 1960s, the greens were bermuda and
to make them fast, the greenkeeper
Surface
Condition Factors
Spatial
Perception
Distance
Perception
-
Space
and the Body
Cerebellum
Role
