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- 1. Unit 5, Chapter 13 CPO Science Foundations of Physics
- 2. Unit 5: Waves and Sound <ul><li>13.1 Harmonic Motion </li></ul><ul><li>13.2 Why Things Oscillate </li></ul><ul><li>13.3 Resonance and Energy </li></ul>Chapter 13 Harmonic Motion
- 3. Chapter 13 Objectives <ul><li>Identify characteristics of harmonic motion, such as cycles, frequency, and amplitude. </li></ul><ul><li>Determine period, frequency, and amplitude from a graph of harmonic motion. </li></ul><ul><li>Use the concept of phase to compare the motion of two oscillators. </li></ul><ul><li>Describe the characteristics of a system that lead to harmonic motion. </li></ul><ul><li>Describe the meaning of natural frequency. </li></ul><ul><li>Identify ways to change the natural frequency of a system. </li></ul><ul><li>Explain harmonic motion in terms of potential and kinetic energy. </li></ul><ul><li>Describe the meaning of periodic force. </li></ul><ul><li>Explain the concept of resonance and give examples of resonance. </li></ul>
- 4. Chapter 13 Vocabulary Terms <ul><li>harmonic motion </li></ul><ul><li>cycle </li></ul><ul><li>period </li></ul><ul><li>frequency </li></ul><ul><li>amplitude </li></ul><ul><li>hertz (Hz) </li></ul><ul><li>damping </li></ul><ul><li>periodic motion </li></ul><ul><li>periodic force </li></ul><ul><li>resonance </li></ul><ul><li>phase </li></ul><ul><li>phase difference </li></ul><ul><li>equilibrium </li></ul><ul><li>restoring force </li></ul><ul><li>stable equilibrium </li></ul><ul><li>unstable equilibrium </li></ul><ul><li>oscillator </li></ul><ul><li>natural frequency </li></ul><ul><li>steady state </li></ul><ul><li>piezoelectric effect </li></ul>
- 5. 13.1 Harmonic motion <ul><li>Key Question: </li></ul><ul><li>How do we describe the back and forth motion of a pendulum? </li></ul>*Students read Section 13.1 AFTER Investigation 13.1
- 6. 13.1 Cycles, systems, and oscillators <ul><li>A cycle is a unit of motion that repeats. </li></ul>
- 7. 13.1 Harmonic motion is common sound communications clocks nature
- 9. 13.1 Amplitude <ul><li>Amplitude describes the size of a cycle. </li></ul>
- 10. 13.1 Amplitude <ul><li>The energy of an oscillator is proportional to the amplitude of the motion. </li></ul><ul><li>Friction drains energy away from motion and slows the pendulum down. </li></ul><ul><li>Damping is the term used to describe this loss. </li></ul>
- 11. 13.1 Linear Motion vs. Harmonic Motion Graphs
- 13. 13.1 Circles and the phase of harmonic motion <ul><li>Circular motion is very similar to harmonic motion . </li></ul><ul><li>Rotation is a cycle, just like harmonic motion. </li></ul><ul><li>One key difference is that cycles of circular motion always have a length of 360 degrees. </li></ul>
- 14. 13.1 Circles and the phase of harmonic motion <ul><li>The word “ phase” means where the oscillator is in the cycle. </li></ul><ul><li>The concept of phase is important when comparing one oscillator with another. </li></ul>
- 15. 13.2 Why Things Oscillate <ul><li>Key Question: </li></ul><ul><li>What kinds of systems oscillate? </li></ul>*Students read Section 13.2 AFTER Investigation 13.2
- 16. 13.2 Why Things Oscillate <ul><li>Systems that have harmonic motion move back and forth around a central or equilibrium position. </li></ul><ul><li>Equilibrium is maintained by restoring forces . </li></ul><ul><li>A restoring force is any force that always acts to pull the system back toward equilibrium. </li></ul>
- 17. 13.2 Inertia <ul><li>Newton’s first law explains why harmonic motion happens for moving objects. </li></ul><ul><li>According to the first law, an object in motion stays in motion unless acted upon by a force. </li></ul>
- 18. 13.2 Stable and unstable systems <ul><li>Not all systems in equilibrium show harmonic motion when disturbed. </li></ul><ul><li>In unstable systems there are forces that act to pull the system away from equilibrium when disturbed. </li></ul><ul><li>Unstable systems do not usually result in harmonic motion (don't have restoring forces). </li></ul>
- 19. 13.2 The natural frequency <ul><li>The natural frequency is the frequency at which systems tend to oscillate when disturbed. </li></ul><ul><li>Everything that can oscillate has a natural frequency, and most systems have more than one. </li></ul>Adding a steel nut greatly increases the inertia of a stretched rubber band, so the natural frequency decreases.
- 20. 13.2 Changing the natural frequency <ul><li>The natural frequency is proportional to the acceleration of a system. </li></ul><ul><li>Newton’s second law can be applied to see the relationship between acceleration and natural frequency. </li></ul>
- 21. 13.3 Resonance and Energy <ul><li>Key Question: </li></ul><ul><li>What is resonance and why is it important? </li></ul>*Students read Section 13.3 AFTER Investigation 13.3
- 22. 13.3 Resonance and Energy <ul><li>Harmonic motion involves both potential energy and kinetic energy . </li></ul><ul><li>Oscillators like a pendulum, or a mass on a spring, continually exchange energy back and forth between potential and kinetic. </li></ul>
- 23. 13.3 Resonance <ul><li>A good way to understand resonance is to think about three distinct parts of any interaction between a system and a force. </li></ul>
- 24. 13.3 Energy, resonance and damping <ul><li>Steady state is a balance between damping from friction and the strength of the applied force. </li></ul><ul><li>Dribbling a basketball on a floor is a good example of resonance with steady state balance between energy loss from damping and energy input from your hand. </li></ul>
- 25. Application: Quartz Crystals

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