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Fundamentals of Physics

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Presentation on theme: "Fundamentals of Physics"— Presentation transcript:

1 Fundamentals of Physics
Chapter 13 Oscillations Oscillations Simple Harmonic Motion Velocity of SHM Acceleration of SHM The Force Law for SHM Energy in SHM An Angular Simple Harmonic Oscillator Pendulums The Simple Pendulum The Physical Pendulum Measuring “g” SHM & Uniform Circular Motion Damped SHM Forced Oscillations & Resonance Physics 2111, 2008 Fundamentals of Physics

2 Fundamentals of Physics
Oscillations Oscillations - motions that repeat themselves. Oscillation occurs when a system is disturbed from a position of stable equilibrium. Clock pendulums swing Boats bob up and down Guitar strings vibrate Diaphragms in speakers Quartz crystals in watches Air molecules Electrons Etc. Physics 2111, 2008 Fundamentals of Physics

3 Fundamentals of Physics
Oscillations Oscillations - motions that repeat themselves. Physics 2111, 2008 Fundamentals of Physics

4 Simple Harmonic Motion
Harmonic Motion - repeats itself at regular intervals (periodic). Frequency - # of oscillations per second 1 oscillation / s = 1 hertz (Hz) Period - time for one complete oscillation (one cycle) T T Physics 2111, 2008 Fundamentals of Physics

5 Simple Harmonic Motion
Position Time Physics 2111, 2008 Fundamentals of Physics

6 Simple Harmonic Motion
Angles are in radians. Physics 2111, 2008 Fundamentals of Physics

7 Amplitude, Frequency & Phase
The frequency of SHM is independent of the amplitude. Physics 2111, 2008 Fundamentals of Physics

8 Velocity & Acceleration of SHM
The phase of v(t) is shifted ¼ period relative to x(t), In SHM, a(t) is proportional to x(t) but opposite in sign. Physics 2111, 2008 Fundamentals of Physics

9 Fundamentals of Physics
The Force Law for SHM Simple Harmonic Motion is the motion executed by a particle of mass m subject to a force proportional to the displacement of the particle but opposite in sign. Hooke’s Law: “Linear Oscillator”: F ~ - x SimpleHarmonicMotion/HorizSpring.html Physics 2111, 2008 Fundamentals of Physics

10 The Differential Equation that Describes SHM
Simple Harmonic Motion is the motion executed by a particle of mass m subject to a force proportional to the displacement of the particle but opposite in sign Hooke’s Law! Newton’s 2nd Law: The general solution of this differential equation is: Physics 2111, 2008 Fundamentals of Physics

11 Fundamentals of Physics
What is the frequency? k = 7580 N/m m = kg f = ? Physics 2111, 2008 Fundamentals of Physics

12 xm without m falling off?
m = 1.0 kg M = 10 kg k = 200 N/m ms = 0.40 Maximum xm without slipping Physics 2111, 2008 Fundamentals of Physics

13 Simple Harmonic Motion
SimpleHarmonicMotion/HorizSpring.html Physics 2111, 2008 Fundamentals of Physics

14 Vertical Spring Oscillations
Physics 2111, 2008 Fundamentals of Physics

15 Energy in Simple Harmonic Motion
Physics 2111, 2008 Fundamentals of Physics

16 Energy in Simple Harmonic Motion
range of motion turning point turning point Physics 2111, 2008 Fundamentals of Physics

17 Gravitational Pendulum
Simple Pendulum: a bob of mass m hung on an unstretchable massless string of length L. SimpleHarmonicMotion/pendulum Physics 2111, 2008 Fundamentals of Physics

18 Simple Pendulum SHM for small q
Simple Pendulum: a bob of mass m hung on an unstretchable massless string of length L. acceleration ~ - displacement SHM SHM for small q Physics 2111, 2008 Fundamentals of Physics

19 A pendulum leaving a trail of ink:
Physics 2111, 2008 Fundamentals of Physics

20 acceleration ~ - displacement SHM
Physical Pendulum A rigid body pivoted about a point other than its center of mass (com). SHM for small q Pivot Point acceleration ~ - displacement SHM Center of Mass quick method to measure g Physics 2111, 2008 Fundamentals of Physics

21 Angular Simple Harmonic Oscillator
Torsion Pendulum: t ~ q Hooke’s Law Spring: Physics 2111, 2008 Fundamentals of Physics

22 Simple Harmonic Motion
Any Oscillating System: “inertia” versus “springiness” Physics 2111, 2008 Fundamentals of Physics

23 SHM & Uniform Circular Motion
The projection of a point moving in uniform circular motion on a diameter of the circle in which the motion occurs executes SHM. The execution of uniform circular motion describes SHM. Physics 2111, 2008 Fundamentals of Physics

24 SHM & Uniform Circular Motion
The reference point P’ moves on a circle of radius xm. The projection of xm on a diameter of the circle executes SHM. radius = xm x(t) UC Irvine Physics of Music Simple Harmonic Motion Applet Demonstrations Physics 2111, 2008 Fundamentals of Physics

25 SHM & Uniform Circular Motion
The reference point P’ moves on a circle of radius xm. The projection of xm on a diameter of the circle executes SHM. x(t) v(t) a(t) radius = xm Physics 2111, 2008 Fundamentals of Physics

26 SHM & Uniform Circular Motion
The projection of a point moving in uniform circular motion on a diameter of the circle in which the motion occurs executes SHM. Measurements of the angle between Callisto and Jupiter: Galileo (1610) earth planet Physics 2111, 2008 Fundamentals of Physics

27 Fundamentals of Physics
Damped SHM SHM in which each oscillation is reduced by an external force. Restoring Force SHM Damping Force In opposite direction to velocity Does negative work Reduces the mechanical energy Physics 2111, 2008 Fundamentals of Physics

28 differential equation
Damped SHM differential equation Physics 2111, 2008 Fundamentals of Physics

29 Damped Oscillations 2nd Order Homogeneous Linear Differential Equation: Eq Solution of Differential Equation: where: b = 0  SHM Physics 2111, 2008 Fundamentals of Physics

30 Damped Oscillations “the natural frequency”
Exponential solution to the DE Physics 2111, 2008 Fundamentals of Physics

31 Fundamentals of Physics
Auto Shock Absorbers Typical automobile shock absorbers are designed to produce slightly under-damped motion Physics 2111, 2008 Fundamentals of Physics

32 Fundamentals of Physics
Forced Oscillations Each oscillation is driven by an external force to maintain motion in the presence of damping: wd = driving frequency Physics 2111, 2008 Fundamentals of Physics

33 “the natural frequency”
Forced Oscillations Each oscillation is driven by an external force to maintain motion in the presence of damping. 2nd Order Inhomogeneous Linear Differential Equation: “the natural frequency” Physics 2111, 2008 Fundamentals of Physics

34 Forced Oscillations & Resonance
2nd Order Homogeneous Linear Differential Equation: Steady-State Solution of Differential Equation: where: w = natural frequency wd = driving frequency Physics 2111, 2008 Fundamentals of Physics

35 Forced Oscillations & Resonance
The natural frequency, w, is the frequency of oscillation when there is no external driving force or damping. less damping more damping w = natural frequency wd = driving frequency When w = wd resonance occurs! Physics 2111, 2008 Fundamentals of Physics

36 Fundamentals of Physics
Oscillations Physics 2111, 2008 Fundamentals of Physics

37 Fundamentals of Physics
Resonance Physics 2111, 2008 Fundamentals of Physics

38 Stop the SHM caused by winds on a high-rise building
400 ton weight mounted on a spring on a high floor of the Citicorp building in New York. The weight is forced to oscillate at the same frequency as the building but 180 degrees out of phase. Physics 2111, 2008 Fundamentals of Physics

39 Forced Oscillations & Resonance
Mechanical Systems e.g. the forced motion of a mass on a spring Electrical Systems e.g. the charge on a capacitor in an LRC circuit Physics 2111, 2008 Fundamentals of Physics


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