chapter13.1_13.2_slides

# chapter13.1_13.2_slides - Course Evaluation Open now till...

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11/29/2009 1 Course Evaluation - Open now till Dec 12 - Please log on to https://ubcats.cas.buffalo.edu to complete your evaluation. - Thanks for your feedback. Chapter 13. Vibrations and Waves

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11/29/2009 2 Vibration (oscillation): Periodic motion Repetitive variation of some quantities (e.g., displacement) in time about a central value Simplest example: mass on a spring Vibrations and waves are everywhere In PHY 102, we will learn that all matters are also waves, called matter wave (yes, including you!). Let’s study the simplest oscillation, mass on a spring The mass move repetitively because the spring applies a periodically varying force on it Hooke’s Law: F s = - k x - F s : spring force - k: spring constant (measures the stiffness of the spring Unit of k: N/m - x: displacement of the object from its equilibrium position; x = 0 is the equilibrium position - Negative sign: the force is always directed opposite to the displacement
3 The force always acts toward the equilibrium position Called the restoring force The direction of the restoring force : the object is being pushed or pulled toward the equilibrium position When x is positive (to the right), F is negative (to the left) When x = 0 (at equilibrium), F is 0 When x is negative (to the left), F is positive (to the right) (Animation) A simple technique to measure the spring constant After a ball of mass 0.55 kg is attached to a spring, it’s length is increased by 0.02 m. Calculate the spring constant of the spring. Solution: Spring force: Gravitational force: Equilibrium condition: 2cm kd d k F s ) ( mg F g y 0 s g F F 0 kd mg d mg k N/m 10 7 . 2 02 . 0 8

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## This note was uploaded on 01/02/2010 for the course PHY 101 taught by Professor Pralle during the Spring '08 term at SUNY Buffalo.

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chapter13.1_13.2_slides - Course Evaluation Open now till...

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