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Unformatted text preview: Lecture 18 Purdue University, Physics 220 1 Midterm Exam 2 March 29, 7:308:30 pm, STEW 183 will cover Chapters 610. Lecture 18 Purdue University, Physics 220 2 Lecture 18 Elasticity and Oscillations PHYSICS 220 Lecture 4 Purdue University, Physics 220 3 Contact Force: Spring Force exerted by a spring is directly proportional to the amount by which it is stretched or compressed. F spring =  k x always trying to restore its original length Lecture 18 Purdue University, Physics 220 4 Hookes Law Revisited Hookes Law F/A = Y * L/L k = Y A/L Y (Youngs Modules) independent of L or A Has the unit of (N/m 2 ) pressure (i.e., pascal) Inherent stiffness of a material For many materials, Y is the same for compression and tension, elastic constant Stress = Y*Strain Define Strain = L / L Stress = F/A F =  k L; where k depends on size of the bar and material Lecture 18 Purdue University, Physics 220 5 Beyond Hooks Law Deformed beyond elastic limit material will no longer return to its original length even when F is completely removed. Lecture 18 Purdue University, Physics 220 6 Simple Harmonic Oscillation The force exerted by a spring is proportional to the distance the spring is stretched or compressed from its relaxed position. F X = k x x is the displacement from the relaxed position and k is the constant of proportionality. Lecture 18 Purdue University, Physics 220 7 Potential Energy in Spring Force of spring is conservative F = k x PE = W W =  k x 2 PE= k x 2 Work done only depends on initial and final position Force x work Lecture 18 Purdue University, Physics 220 8 Energy Conservation A mass is attached to a spring and set to motion. The maximum displacement is motion....
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This note was uploaded on 04/10/2011 for the course PHYS 220 taught by Professor Chang during the Spring '09 term at Purdue UniversityWest Lafayette.
 Spring '09
 CHANG
 Physics, Force

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