54. Considering an undamped, forced oscillator (b 0), show that Equation 15.35 is a solution of Equation 15.34, with an amplitude given by Equation 15.36. A common example of a forced oscillator is a damped oscillator driven by an external force that varies periodically, such as F(t) = F, sin wt, where F, is a constant and w is the angular frequency of the driving force. In general, the frequency w of the driving force is variable, whereas the natural frequency w, of the oscillator is fixed by the values of k and m. Modeling an oscillator with both retarding and driv- ing forces as a particle under a net force, Newton's second law in this situation gives d'x EF = ma, F, sin wt- b dx - kx = m dt (15.34) dt2 Again, the solution of this equation is rather lengthy and will not be presented. After the driving force on an initially stationary object begins to act, the ampli- tude of the oscillation will increase. The system of the oscillator and the surround- ing medium is a nonisolated system: work is done by the driving force, such that the vibrational ener of the system (kinetic energy of the object, elastic potential energy in the spring) and internal energy of the object and the medium increase. After a sufficiently long period of time, when the energy input per cycle from the driving force equals the amount of mechanical energy transformed to internal energy for cach cycle, a steady-state condition is reached in which the oscillations proceed with constant amplitude. In this situation, the solution of Equation 15.34 is x = A cos (wt + 6) (15.35) where Amplitude of a > (15.36) bo (? - w,?) + driven oscillator and where w, = Vk/m is the natural frequency of the undamped oscillator (b = 0).
54. Considering an undamped, forced oscillator (b 0), show that Equation 15.35 is a solution of Equation 15.34, with an amplitude given by Equation 15.36. A common example of a forced oscillator is a damped oscillator driven by an external force that varies periodically, such as F(t) = F, sin wt, where F, is a constant and w is the angular frequency of the driving force. In general, the frequency w of the driving force is variable, whereas the natural frequency w, of the oscillator is fixed by the values of k and m. Modeling an oscillator with both retarding and driv- ing forces as a particle under a net force, Newton's second law in this situation gives d'x EF = ma, F, sin wt- b dx - kx = m dt (15.34) dt2 Again, the solution of this equation is rather lengthy and will not be presented. After the driving force on an initially stationary object begins to act, the ampli- tude of the oscillation will increase. The system of the oscillator and the surround- ing medium is a nonisolated system: work is done by the driving force, such that the vibrational ener of the system (kinetic energy of the object, elastic potential energy in the spring) and internal energy of the object and the medium increase. After a sufficiently long period of time, when the energy input per cycle from the driving force equals the amount of mechanical energy transformed to internal energy for cach cycle, a steady-state condition is reached in which the oscillations proceed with constant amplitude. In this situation, the solution of Equation 15.34 is x = A cos (wt + 6) (15.35) where Amplitude of a > (15.36) bo (? - w,?) + driven oscillator and where w, = Vk/m is the natural frequency of the undamped oscillator (b = 0).
College Physics
11th Edition
ISBN:9781305952300
Author:Raymond A. Serway, Chris Vuille
Publisher:Raymond A. Serway, Chris Vuille
Chapter13: Vibrations And Waves
Section: Chapter Questions
Problem 32P: A spring of negligible mass stretches 3.00 cm from its relaxed length when a force of 7.50 N is...
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