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Physics 101: Lecture 10 Application of Newton's Laws

Physics 101: Lecture 10 Application of Newton's Laws. New Material: Textbook Chapter 5 Circular Motion & Centripetal Acceleration. You are twirling a ball on string. What happens if the string breaks ?. b. c. a. v. Answer: b.  v. v 1. v 2. v 2. R. v 1.  R.

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Physics 101: Lecture 10 Application of Newton's Laws

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  1. Physics 101: Lecture 10Application of Newton's Laws • New Material: Textbook Chapter 5 • Circular Motion & Centripetal Acceleration

  2. You are twirling a ball on string.What happens if the string breaks ? b c a v Answer: b

  3. v v1 v2 v2 R v1 R centripetal acceleration Acceleration in Uniform Circular Motion(circular motion with constant speed) aave= Dv / Dt Uniform motion: magnitudes of v1,v2 are equal: v1=v2=v Distance traveled (small Dt) : DR = v Dt Similar triangles: DR/R = Dv/v => Dv/Dt= v2/R

  4. centripetal acceleration Uniform Circular Motion(circular motion with constant speed) R v a • Instantaneous velocity is tangent to circle • Instantaneous acceleration is radially inward • There must be a force to provide the acceleration

  5. correct a=v2/R R FN v mg SF = ma = mv2/R SF = FN - mg=mv2/R FN = mg + mv2/R Example: Circular Motion Suppose you are driving through a valley whose bottom has a circular shape. If your mass is m, what is the magnitude of the normal force FN exerted on you by the car seat as you drive past the bottom of the hill1. FN < mg2. FN = mg3. FN > mg When level your normal force = your weight Since there is centripetal acceleration, the normal force is greater than simply mg.

  6. Centripetal Force Centripetal acceleration: Acceleration is the result of a net-force acting on an object. In case of ac this net-force is called centripetal force, Fc: Magnitude of Fc: Fc= S F= m ac= m v2/R Define frequency f, period T, angular velocity w:

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