physics chp t 13

8/10/2019 Physics Chp t 13

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Un it 5, Ch apter 13

CPO Sc ien c e

Fou nd at ion s o f Phy s ics


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Unit 5: Waves and Sound

13.1 Harmonic Motion

13.2 Why Things Oscillate

13.3 Resonance and Energy

Chapter 13 Harmonic Motion


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Chapter 13 Objectives1. Identify characteristics of harmonic motion, such as cycles,frequency, and amplitude.

2. Determine period, frequency, and amplitude from a graph ofharmonic motion.

3. Use the concept of phase to compare the motion of twooscillators.

4. Describe the characteristics of a system that lead to harmonicmotion.

5. Describe the meaning of natural frequency.6. Identify ways to change the natural frequency of a system.7. Explain harmonic motion in terms of potential and kinetic energy.8. Describe the meaning of periodic force.9. Explain the concept of resonance and give examples of

resonance.


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Chapter 13 Vocabulary Termsharmonic motioncycleperiodfrequencyamplitudehertz (Hz)dampingperiodic motionperiodic forceresonance

phasephase differenceequilibriumrestoring forcestable equilibriumunstable equilibriumoscillatornatural frequencysteady statepiezoelectric effect


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13.1 Cycles, systems, and oscillatorsA cycle is a unit of motion that repeats.


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13.1 Harmonic motion is commonsound communications

clocks

nature


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13.1 AmplitudeAmplitude describes the size of a cycle.


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13.1 AmplitudeThe energy of an oscillator is proportional to the

amplitude of the motion.

Friction drains energy away from motion and slowsthe pendulum down.

Damping is the term used to describe this loss.


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13.1 Linear Motion vs. Harmonic MotionGraphs


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13.1 Circles and the phaseof harmonic motionCircular motion is very similar to

harmonic motion .Rotation is a cycle, just likeharmonic motion.

One key difference is that cyclesof circular motion always have alength of 360 degrees.


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13.1 Circles and the phaseof harmonic motionThe word phase means where the oscillator is in thecycle.The concept of phase is important when comparing oneoscillator with another.


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13.2 Why Things Oscillate

Key Question:

What kinds of systemsoscillate?

*Students read Section 13.2AFTER Investigation 13.2


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13.2 Why Things OscillateSystems that have harmonicmotion move back and fortharound a central or equilibrium position.

Equilibrium is maintained byrestoring forces .

A restoring force is any force thatalways acts to pull the system backtoward equilibrium.


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13.2 InertiaNewtons first law explains why harmonic motionhappens for moving objects.According to the first law, an object in motion stays inmotion unless acted upon by a force.


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13.2 Stable and unstable systemsNot all systems in equilibrium show harmonic motionwhen disturbed.In unstable systems there are forces that act to pull thesystem away from equilibrium when disturbed.Unstable systems do not usually result in harmonicmotion (don't have restoring forces).


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13.2 The natural frequencyThe natural frequency is thefrequency at which systemstend to oscillate whendisturbed.

Everything that can oscillatehas a natural frequency, andmost systems have morethan one.

A dd ing a s teel nu t great ly inc reases th e iner t ia of a

st retch ed rub ber band, so th e natural f requ ency d ecreases .


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13.2 Changing the natural frequencyThe natural frequency is proportional to the accelerationof a system.Newtons second law can be applied to see therelationship between acceleration and natural frequency.


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13.3 Resonance and Energy

Key Question:

What is resonance andwhy is it important?

*Students read Section 13.3AFTER Investigation 13.3


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13.3 Resonance and EnergyHarmonic motion involves both potential energy andkinetic energy .Oscillators like a pendulum, or a mass on a spring,continually exchange energy back and forth betweenpotential and kinetic.


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13.3 Resonance A good way to understand resonance is to thinkabout three distinct parts of any interaction

between a system and a force.


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13.3 Energy, resonance and dampingSteady state is a balance between damping fromfriction and the strength of the applied force.

Dribbling a basketball on afloor is a good example ofresonance with steady statebalance between energy lossfrom damping and energyinput from your hand.


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Application: Quartz Crystals

physics chp t 13

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