151-M1 Handout rev 2

151-M1 Handout rev 2 - M1 Friction I. Objective PHY 151...

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1 M1 Friction PHY 151 I. Objective Verify that the frictional force f is proportional to the normal reaction force F N. Determine the coefficients of static and kinetic friction for two types of surfaces. II Equipment Adjustable incline plane, Teflon bottom pan, rubber bottom pan, dial spring scale, weights, 100 cm ruler, plumb bob. III. Introduction When two objects are in contact they exert “contact forces” on each other. For example in fig.1 we show the two components of the contact force exerted by the floor on a block of mass m on which a horizontal force F is acting. One component labeled “ F N ” in fig.1 is normal (perpendicular) to the contact interface between the floor and the block. The other component labeled “ f ” in fig.1 is parallel to the contact interface and is known as “friction”. Friction always opposes motion (real or impending). The magnitude of f is proportional to the magnitude of F N . If the block is moving with respect to the floor then the frictional force is called “kinetic” (symbol k f ) and its magnitude is given by the equation: kk N f F (1) The constant k is known as the “coefficient of kinetic friction” and depends on the nature of the two objects in contact. This constant does not depend on the magnitude of the normal force ( F N ) or applied forces. If the block is not moving with respect to the floor then the frictional force is called “static” (symbol S f ) and its magnitude is given by the inequality: 0 s SN f F (2) F N mg F f Fig.1
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2 In other words S f can take a range of values from a minimum value of 0 to a maximum value of : max SS N f F (3) IV. Experimental Method A. Coefficient of kinetic friction
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151-M1 Handout rev 2 - M1 Friction I. Objective PHY 151...

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