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SOLUTIONS
, Contents
1 Free Oscillations of a Linear Oscillator
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1.2 Review of the Principal Formulas ........................................................... 5
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1.3 Questions and Problems with Answers and Solutions............................... 6
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1.3.1 Free Undamped Oscillations ....................................................... 6
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1.3.2 Damped Free Oscillations ........................................................ 11
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1.3.3 Non-oscillatory Motion of the System ...................................... 15 c c c c
2 Torsion Spring Oscillator with Dry Friction
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2.2 Review of the Principal Formulas ......................................................... 21
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2.3 Questions and Problems with Answers and Solutions............................. 22
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2.3.1 Damping Caused by Dry Friction ............................................ 22
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2.3.2 Influence of Viscous Friction ................................................... 26
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3 Forced Oscillations in a Linear System
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3.4 Review of the Principal Formulas ......................................................... 31
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3.5 Questions and Problems with Answers and Solutions............................. 32
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3.5.1 Steady-state Forced Oscillations ............................................... 32 c c
3.5.2 Transient Processes ................................................................. 44
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4 Square-wave Excitation of a Linear Oscillator
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4.8 Review of the Principal Formulas ......................................................... 59
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4.9 Questions and Problems with Answers and Solutions ............................ 60
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4.9.1 Swinging of the Oscillator at Resonance .................................. 60
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4.9.2 Non-resonant Forced Oscillations ............................................ 69 c c
5 Parametric Excitation of Oscillations
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5.4 Questions and Problems with Answers and Solutions ............................ 75
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5.4.1 Principal Parametric Resonance............................................... 75
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5.4.2 Manual Control of the Parameter ............................................. 90
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5.4.3 Parametric Resonances of High Orders..................................... 91
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, 4 CONTENTS
6 Sinusoidal Modulation of the Parameter
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6.4 Questions and Problems with Answers and Solutions ........................... 103
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6.4.1 Principal Parametric Resonance ............................................. 103
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6.4.2 The Principal Interval of Parametric Resonance ...................... 109
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6.4.3 The Second Parametric Resonance ......................................... 113
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7 Free Oscillations of the Rigid Pendulum
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7.5 Review of the Principal Formulas ........................................................ 115
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7.6 Questions and Problems with Answers and Solutions ........................... 116
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7.6.1 Small Oscillations of the Pendulum ....................................... 116
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7.6.2 Oscillations with Large Amplitudes ....................................... 121
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7.6.3 The Rotating Pendulum ......................................................... 133
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, Chapter 1 c
FreeOscillations ofaLinear c c c c
Oscillator
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1.2 Review of the Principal Formulas c c c c
The differential equation of a free linear torsion oscillator:
c c c c c c c c
ϕ¨ + 2γϕ˙ + ω02ϕ = 0.
c c c c c c (1.1)
c c free oscillations without friction (at γ ≪ ω0):
The frequency and the period of√ c c c c c
c
c c c c c c c
D 2π c
ω0 = , T0 = . (1.2) c c c c
J ω0
An oscillatory solution (valid at γ < ω0):
c c c c c c c
ϕ(t) = A0e−γt cos(ω1t + δ0),
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where the constants A0 and δ0 aredetermined by the initial conditions ϕ(0), ϕ˙(0).
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The frequency ω1 of damped oscillations
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√
ω1 = ω20− γ2. (1.4) c c c c
Anequivalent formofthe generalsolution:
c c c c c c
−
ϕ(t) c = e γt
(C cosω1t + S sinω1t),
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where the constants C and S are determined by the initial conditions. They are
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related to A0 and δ0:
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√
A0 = C2 + S2, tanδ0 = −S/C. (1.6) c c
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