Prof. Matt Jarvis [email protected] Hilary Term 2015
Transcript of Prof. Matt Jarvis [email protected] Hilary Term 2015
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Spring-mass systems
Now consider a horizontal system in the form of masses on springs • Again solve via decoupling and matrix
methods • Obtain the energy within the system • Find specific solutions
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Solutions of horizontal spring-mass system Equations of motion:
Solve by decoupling method (add 1 and 2 and subtract 2 from 1). As before, we can write down the normal coordinates, call them q1 and q2
which means…
Substituting gives:
(1)
(2)
Gives normal frequencies of:
Centre of Mass Relative
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Total Energy:
Energy of horizontal spring-mass system Kinetic Energy Potential Energy
Sum of energies in each normal mode
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Specific Solutions for horizontal spring-mass system
General solution is the sum of the two normal modes
Initial conditions:
These give:
Both normal modes excited. The `beats’ solution. Completely analogous to the coupled pendulum
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Decoupling method only works for limited cases with a sufficient amount of symmetry. You cannot solve this with decoupling, so have to go to matrix method and have a guess!
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Coupled Oscillators with a driving force
• So the last physical system we are going to look at in this first part of the course is the forced coupled pendula, along with a damping factor 1. Finding the Complementary Function 2. Finding the particular integral
• Then do the same for a horizontal spring-
mass system
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There is no physical difference between +/- variants. Just use + from now on.
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