lecture-ch6 - Contents 6 Friction, Drag, and Centripetal...

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Unformatted text preview: Contents 6 Friction, Drag, and Centripetal Force 1 6.1 Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 6.2 The Drag Force and Terminal Speed . . . . . . . . . . . . . . 2 6.3 Uniform Circular Motion . . . . . . . . . . . . . . . . . . . . . 5 6.3.1 Rounding a curve in a car . . . . . . . . . . . . . . . . 5 6.3.2 Orbiting Earth . . . . . . . . . . . . . . . . . . . . . . 5 6.3.3 More Examples . . . . . . . . . . . . . . . . . . . . . . 6 6 Friction, Drag, and Centripetal Force 6.1 Friction vector f s vector F N vector F g vector F Static friction force: In the above figure, vector F N is the normal force and vector F is the horizontal external force acting on the body. The friction force vector f s is equal to- vector F when vextendsingle vextendsingle vextendsingle vector F vextendsingle vextendsingle vextendsingle , the magnitude of the external force is less than vextendsingle vextendsingle vextendsingle vector F vextendsingle vextendsingle vextendsingle < f s, max = μ s F N where μ s is the coefficient of static friction , otherwise the body begins to accelerate. 1 Kinetic friction force: vector f k vector F N vector F g vector F If the body begins to move, the friction force becomes vector f k =- μ k F N vector F vextendsingle vextendsingle vextendsingle vector F vextendsingle vextendsingle vextendsingle where μ k is the coefficient of kinetic friction . Note that the magnitude of vector f k is proportional to the normal force. f k = μ k F N ABS: anti-lock braking system ? Usually μ k < μ s , if tires are locked, μ k comes into play and lengthens the braking distance. 6.2 The Drag Force and Terminal Speed When there is a relative motion between a fluid and a body, the body ex- periences a drag force vector D that opposes the relative motion and points in the direction in which the fluid flows relative to the body....
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lecture-ch6 - Contents 6 Friction, Drag, and Centripetal...

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