23 Mar, 2012
PRESENTATION: When relative movement exists between two rigid systems, opposition appears if they are not polished. This friction force depends essentially on the material and the surface finish of the rigid systems, and on the perpendicular reaction at the surfaces.
- Revisiting the Least Force Required to Keep a Block from Sliding, Subhranil De, Phys. Teach. 51, 220 (2013)
- Removing Coins from a Dice Tower: No Magic — Just Physics, Michael Vollmer and Klaus-Peter Möllmann, Phys. Teach. 51, 212 (2013)
- Analyzing radial acceleration with a smartphone acceleration sensor, Patrik Vogt and Jochen Kuhn, Phys. Teach. 51, 182 (2013)
INTRODUCTION: The force of friction between two bodies appears even when there is no relative accelerated movement between them. When this happens the static friction force is acting, which is usually written as Fre, and its magnitude can take values between zero and a maximum, which is given by:
OBJECTIVE: To show experimentally that the relationship between the velocity of a certain body and its static friction influence its state of rest or movement.
MATERIALS: rotating table, coins, chronometer.
SETUP: The centre of the table is located and the radius marked. Coins are placed along the mark and their contours are drawn around.
EXPLANATION: Static friction provides the coins with centripetal force. By placing a line of coins along the radius of a spinning table, the most outlying one in the line that does not fly off the turning surface is the one experiencing the maximum force of static friction. For various rotation speeds, the coin that is the first of those that do not fly off can be noted and we can see how the distance of the coin from the axis and the velocity satisfy the relation:
CONCEPTS: static friction, centripetal acceleration, period, rotation velocity, friction force, dynamic friction, weight, normal force.
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STUDENTS 2011-2012: Airas Toba, Bran Touriño, Cristina Varela
LINK pdf STUDENTS (in Spanish):