The Physics Factbook™
Edited by Glenn Elert -- Written by his students
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|Zitzewitz, Paul. Merrill Physics: Principles and Problems. New York: Glencoe, 1995:106.||"You are driving a 2500.0 kg car at a constant speed of 14 m/s along an icy, but straight and level road. While approaching a traffic light, it turns red. You slam on the brakes. Your wheels lock, the tires begin skidding and the car slides to a halt in a distance of 25.0 M. What is the coefficient of sliding friction between your tires and the icy roadbed?"||0.400|
|The University of the State of New York Reference Tables for Physical Setting/Physics. New York: The State Education Department, 2002.||"Kinetic, Rubber on ice, 0.15"||0.15|
|De-Konin-JJ, De-Groot-G, Van-Ingen-Schenau-GJ. "Ice friction during speed skating." Journal of Biomechanics 25, 6. (June 1992): 565-71.||"Special skates were developed and used to measure the ice frictional forces during actual speed skating. The mean coefficients of friction for the straights and curves were, respectively, 0.0046 and 0.0059."||0.0046
|Brown, Ian. Classical Friction. Abrasion and Friction in Parallel-lay Rope Terminations.||
|Babcock, David D. The Coefficient of Kinetic Friction for Curling Ice. 8 April 1996.||"Experimentally obtaining values for the total distance traveled and for the initial velocity of the curling stone with the aid of NIH imaging we calculate the coefficient of kinetic friction for curling ice. We obtain a numerical value which is actually less than that of Teflon on Teflon.
Coefficient of Kinetic Friction
1 -0.251 0.0256
2 -0.131 0.0134
3 -0.178 0.0181
4 -0.134 0.0136
5 -0.130 0.0133
The average of the above coefficient of friction values gives us an experimental value of µk = 0.0168"
Have you ever watched a curling match or speed skating race and wondered how the skaters could fly by with such speed, or the technique involved in curling? Some scientists and those in the game take the study of motion on ice with high concern. One key value they look at is the coefficient of friction for ice, a value which determines the resistance to the sliding of ice across another surface, the edge of a skate or the stone in curling. In litanies of experiments, scientists in the field have determined methods to reduce the coefficient of friction for ice.
Friction is the oppositional force to motion between two surfaces in contact. The two most common types are static and kinetic, or sliding friction. The force of kinetic friction (fk) is much less than that of static friction, since static friction (fs) is the force needed to start an object in motion, whereas kinetic friction merely hinders the motion of an already moving object.
The force of friction depends on two values, the force pushing the surfaces together (FN) and the coefficient of friction (µ). Thus,
Ff = µFN
The coefficient of friction is a constant that depends on the two surfaces in contact. This constant changes when motion begins. Since fs > fk, and the normal force (FN) remains constant, the coefficient of friction of static friction is more than that of kinetic friction. Thus, µs > µk.
The coefficient of ice is relatively low and much less than one. A system with a low coefficient of friction has a low resistance to the surfaces sliding across one another. The fact that ice has a low coefficient of friction can be seen easily by pushing someone across an ice-skating rink. In order for the person to move the push must exceed the frictional force. The slightest nudge will cause the person to slide across the ice, therefore the frictional force is low and through inference the coefficient of friction for ice is minimal as well.
Genna Ableman -- 2004
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