Too much friction leads to sore feet, sore muscles, and, paradoxically, falls from feet catching on the floor. Too little friction means too much of one's concentration goes into not slipping so that one cannot enjoy the dancing. Pivoting with full weight on the front of one foot should feel almost frictionless. Sliding with full weight onone foot should be impossible. What is the right slickness of floor, and how would you know if you had it? The friction depends on the combination of shoe sole and floor wax, not just the floor wax alone.
FRICTION MEASUREMENT. The coefficient of friction is the ratio of the horizontal force to the vertical force when your foot slides on the floor. In a pinch I suppose a bathroom scale alone could provide adequate measurements of both the vertical and horizontal forces, but I have not tried it. To measure horizontal force with a bathroom scale, you would have to re-zero the scale just for the horizontal measurement. A tubular brass spring scale model IN-100-MRP by the Chatillon division of Ametek, 718-847-5000 in Kew Gardens, NY, measures up to 100 lbs and is ideal for measuring the horizontal force of floor friction. See it at http://www.chatillon.com/products/force/spgdyna.html. The vertical force will be measured by you getting on bathroom scales. Wear shoes with the same material for both soles and heels; this is usually soft grey or bluish grey chrome tanned split leather on ballroom dance shoes. Well worn shoes should be used, since new dance shoe soles are sticky. Tie a rope to the spring scale. Stand on one foot, pull horizontally on the scale with the other end of the rope held by two accomplices,or tied to a post. Gradually lean back at a steeper angle until your foot slips and you catch yourself with the other foot. This measurement is very difficult the first time you try it. It is easier on slicker floors. On a good dance floor, the reading indicated by the red slider on the scale should be between 30 and 36 percent of your weight if you pulled slow and steady with no jerking. The middle of this range, 33 percent, is best. Make several measurements until you get practiced and steady, and the measurements are reasonably repeatable. Each measurement should be made on a different spot of floor; repeated rubbing of the same spot can momentarily reduce the friction of that spot on some floor finishes.
The coefficient of friction that starts your foot to sliding is called the coefficient of static friction. The coefficient that keeps your foot sliding at a steady rate is the coefficient of sliding friction. If they are about the same, when your foot starts to slide, you can keep it sliding slowly and steadily for two to four inches. If the coefficient of sliding friction is much lower than the coefficient of static friction, when your foot starts to slide, it will quickly slip out from under you, and you will immediately have to catch yourself with your other foot. For a dance floor to be acceptable, the two coefficients should be about the same. It should be possible to slowly slide your foot at a steady rate. The measurement method presented here provides a number for static friction. Only a qualitative estimate is provided for sliding friction, based on whether you can do a controlled slide or not.