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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
1.3 Questions and Problems with Answers and Solutions .......................... 6
1.3.1 Free Undamped Oscillations ................................................... 6
1.3.2 Damped Free Oscillations ..................................................... 11
1.3.3 Non-oscillatory Motion of the System................................... 15
2 Torsion Spring Oscillator with Dry Friction
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2.2 Review of the Principal Formulas ..................................................... 21
2.3 Questions and Problems with Answers and Solutions ........................ 22
2.3.1 Damping Caused by Dry Friction .......................................... 22
2.3.2 Influence of Viscous Friction ................................................ 26
3 Forced Oscillations in a Linear System
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3.4 Review of the Principal Formulas ..................................................... 31
3.5 Questions and Problems with Answers and Solutions ........................ 32
3.5.1 Steady-state Forced Oscillations ............................................ 32
3.5.2 Transient Processes .............................................................. 44
4 Square-wave Excitation of a Linear Oscillator
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4.8 Review of the Principal Formulas ..................................................... 59
4.9 Questions and Problems with Answers and Solutions ........................ 60
4.9.1 Swinging of the Oscillator at Resonance ............................... 60
4.9.2 Non-resonant Forced Oscillations.......................................... 69
5 Parametric Excitation of Oscillations
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5.4 Questions and Problems with Answers and Solutions ........................ 75
5.4.1 Principal Parametric Resonance............................................ 75
5.4.2 Manual Control of the Parameter ......................................... 90
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
6.4.1 Principal Parametric Resonance .......................................... 103
6.4.2 The Principal Interval of Parametric Resonance ................... 109
6.4.3 The Second Parametric Resonance ...................................... 113
7 Free Oscillations of the Rigid Pendulum
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7.5 Review of the Principal Formulas .................................................... 115
7.6 Questions and Problems with Answers and Solutions....................... 116
7.6.1 Small Oscillations of the Pendulum..................................... 116
7.6.2 Oscillations with Large Amplitudes ..................................... 121
7.6.3 The Rotating Pendulum ...................................................... 133
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, Chapter 1 I l
FreeOscillationsofaLinear lI lI Il lI
Oscillator
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1.2 Review of the Principal Formulas Il Il Il Il
The differential equation of a free linear torsion oscillator:
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ϕ¨ + 2γϕ˙ + ω02ϕ = 0.
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Il Il free oscillations without friction (at γ ≪ ω0):
The frequency and the period of√ Il Il lI lI lI
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ω0 = , T0 = . (1.2) Il lI Il Il
J ω0
An oscillatory solution (valid at γ < ω0):
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ϕ(t) = A0e−γt cos(ω1t + δ0), Il Il Il Il Il (1.3)
wheretheconstantsA0 andδ0 aredeterminedbytheinitialconditionsϕ(0), ϕ˙(0).
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Thefrequencyω1 ofdampedoscillations
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√
ω1 = ω20 − γ2. (1.4) I l Il Il Il
Anequivalentformofthegeneralsolution:
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ϕ(t) Il = e γt
(Ccosω1t+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) I l I l
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