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Physics 101: Lecture 11 Centripetal Force

Physics 101: Lecture 11 Centripetal Force. Brief Review of Chapters 1-4 Textbook Chapter 5 Uniform circular motion : satellites in circular orbits, apparent weightlessness and artificial gravity. Centripetal Force. Centripetal acceleration:.

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Physics 101: Lecture 11 Centripetal Force

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  1. Physics 101: Lecture 11Centripetal Force • Brief Review of Chapters 1-4 • Textbook Chapter 5 • Uniform circular motion : satellites in circular orbits, apparent weightlessness and artificial gravity

  2. 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 Direction of Fc: always points towards the center of the circle Define frequency f, period T, angular velocity w: The period T is the time required to travel once around the circle, ie to make one complete revolution: T=2p R/v

  3. Satellites in Circular Orbits • Satellites in circular orbits are examples of uniform circular motion. What provides the centripetal force ? The gravitational pull of the earth: Fc= G M m/r2 = mv2/r • Orbital speed of statellite : v = (GM/r)1/2 => v does not depend on mass of satellite ! Synchronous satellites: Orbital period T=1 day = time it takes for the earth to turn once around its axis. => Satellite always appears to be at a fixed position in the sky -> stationary relay stations for communication signals sent up from earth.

  4. Synchronous Satellites • To serve as stationary relay station the satellite must be placed at a certain height above the earth surface: T=1 day=8.64 x 104 s = 2p r/v and v=(G M/r)1/2 • r3/2=T (GM)1/2/(2p) => r=4 x 107 m • H=r-rE=3.6 x 107 m = 22300 miles

  5. Circular Motion: More Examples • Apparent weightlessness: Apparent weight in a satellite is zero just as in a free falling elevator : Person and scale fall with the same acceleration towards the center of earth => they cannot push against each other. Artificial Gravity: In a rotating space laboratory a push on A persons feet equal to mg can be simulated by the centripetal force if v = (r g)1/2.

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