ILLEGAL BRUSHING: Page 2 (done by many but usually wrong)

    The drawing below describes the slow and fast side of a rock which is why rocks curl in the direction of turn. Snowplow friction on the slow side is higher than shear friction plus snow plow friction on the fast side. That is, after the pebble is knocked down the rock will curl in the direction of turn. Total friction caused movement (curl) is a function of rock speed. As a rock slows the sheet ice and the running surface ice coating have more time to nucleate/bond -- result= higher friction causing side movement - curl. A point on a rock that is moving slower relative to a spot on the ice moving faster will have the highest friction.
    The sum of the friction forces of each minute particle of the sheet ice bonding to the rock's ice coated running surface on the slow side multiplied by the moment arm distances produce a net lateral force "dragging" the rock in the direction of turn.  Modification of this friction force with high cycle, high PSI, and edge brushing can and will slow or even STOP curl. With the "right" brush fabric (not yet produced on commercial brushes) and high psi (small brush head), quick cycles, and side of rock application,  you can even INCREASE curl. Some pro's do it BUT ON THE WRONG SIDE causing their rock to crash into guards and lose the Worlds!!!
    The secret was released in March of 1999 through the draft copy of "The Book" to the curling commentators who are now alluding to the technique in current cash spiel games. Many major teams (Middaugh) have not picked up on the commentary and have not thrown away their 12" brushes which do no more than clean massive areas of ice un-necessarily while wasting brushing energy (which should be directed at the 5" running surface). They use low psi. and actually brush their rocks into guards! It cost them dearly last weekend at the GMC cash spiel; however, Stoughton was arm boosting takeouts and missing the brush to give Middaugh an undeserved win. It is good to know there is a lot of room for improvement at the pro level so room for the student who is willing to learn, understand, and use Mother Nature's laws to improve their game.


Visual indication as to why rocks curl -- or don't curl?

Bottom View of Rock Running Surface - 5" radius by 1/4-5/16" width



                 Velocity vectors A+C =

Maximum fast side velocity relative to spot on ice
                                                 
                                                 E

Rotational velocity vector E=Tangential vectors C=B           

wpe1.jpg (5770 bytes)
        Right rotation.
Vector B =C in quantity only
Velocity vectors A=A=A== Rock speed relative to side boards.


D vector=A-B
A-B= slowest velocity vector (D) to spot on ice. HIGHEST FRICTION ZONE

"FAST" side of rock running surface.                           "SLOW" side of rock running surface

            Lower friction side.                                                                    Higher friction side.

When slow side friction is higher than the net of cup edge and leading edge "shear" tangential friction, the rock will curl to the right. Slow side friction keeps the rock rotating (as if in perpetual motion) even after a small force is applied to the turn at release. When shear friction is equal or higher as in the case of excessive frost or new large pebble, sharp rocks, (first end), the rock will run straight or even "curl" in the opposite direction of rotation (fall off) because shear friction is more than slow side friction. Like throwing a tire with right turn flat-ways onto pavement -- the tire will dig in to the high friction pavement and "curl" to the left -- opposite to the imparted rotation.
  Right turning rock scenario. The other major contributor to "slow side" friction comes from the actual dragging of snow into the right half of the rock running surface area. Most is "dumped" out the back by forward motion and rock vibration leaving the "fast side" cleaner and smoother=less friction.

  SHEAR FRICTION: See figure of analog gear rock  (also in The Book)

    Shear friction translates into the resistance to turn -- the tangential force on the leading edge which resists the turn and resultant curl. It can quite likely stop the handle/rotation. The rotational resistance can be great enough on new pebble to cause the rock to move in the opposite direction to normal curl!
Good illegal "edge brushing". Now your team should be able to defeat a very fine work together team --  Wayne Middaugh's team! At least until he figures out this brushing technique. 
JKR: The Curling Doctor