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Unit 5, Chapter 13

Unit 5, Chapter 13. CPO Science Foundations of Physics. Unit 5: Waves and Sound. Chapter 13 Harmonic Motion. 13.1 Harmonic Motion 13.2 Why Things Oscillate 13.3 Resonance and Energy. Chapter 13 Objectives.

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Unit 5, Chapter 13

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  1. Unit 5, Chapter 13 CPO Science Foundations of Physics

  2. Unit 5: Waves and Sound Chapter 13 Harmonic Motion • 13.1 Harmonic Motion • 13.2 Why Things Oscillate • 13.3 Resonance and Energy

  3. Chapter 13 Objectives • Identify characteristics of harmonic motion, such as cycles, frequency, and amplitude. • Determine period, frequency, and amplitude from a graph of harmonic motion. • Use the concept of phase to compare the motion of two oscillators. • Describe the characteristics of a system that lead to harmonic motion. • Describe the meaning of natural frequency. • Identify ways to change the natural frequency of a system. • Explain harmonic motion in terms of potential and kinetic energy. • Describe the meaning of periodic force. • Explain the concept of resonance and give examples of resonance.

  4. Chapter 13 Vocabulary Terms • harmonic motion • cycle • period • frequency • amplitude • hertz (Hz) • damping • periodic motion • periodic force • resonance • phase • phase difference • equilibrium • restoring force • stable equilibrium • unstable equilibrium • oscillator • natural frequency • steady state • piezoelectric effect

  5. Key Question: How do we describe the back and forth motion of a pendulum? 13.1 Harmonic motion *Students read Section 13.1 AFTER Investigation 13.1

  6. 13.1 Cycles, systems, and oscillators A cycle is a unit of motion that repeats.

  7. 13.1 Harmonic motion is common communications sound clocks nature

  8. 13.1 Amplitude Amplitude describes the size of a cycle.

  9. 13.1 Amplitude The energy of an oscillator is proportional to the amplitude of the motion. • Friction drains energy away from motion and slows the pendulum down. • Damping is the term used to describe this loss.

  10. 13.1 Linear Motion vs. Harmonic Motion Graphs

  11. 13.1 Circles and the phase of harmonic motion • Circular motion is very similar to harmonic motion. • Rotation is a cycle, just like harmonic motion. • One key difference is that cycles of circular motion always have a length of 360 degrees.

  12. 13.1 Circles and the phase of harmonic motion • The word “phase” means where the oscillator is in the cycle. • The concept of phase is important when comparing one oscillator with another.

  13. Key Question: What kinds of systems oscillate? 13.2 Why Things Oscillate *Students read Section 13.2 AFTER Investigation 13.2

  14. 13.2 Why Things Oscillate • Systems that have harmonic motion move back and forth around a central or equilibrium position. • Equilibrium is maintained by restoring forces. • A restoring force is any force that always acts to pull the system back toward equilibrium.

  15. 13.2 Inertia • Newton’s first law explains why harmonic motion happens for moving objects. • According to the first law, an object in motion stays in motion unless acted upon by a force.

  16. 13.2 Stable and unstable systems • Not all systems in equilibrium show harmonic motion when disturbed. • In unstable systems there are forces that act to pull the system away from equilibrium when disturbed. • Unstable systems do not usually result in harmonic motion (don't have restoring forces).

  17. 13.2 The natural frequency • The natural frequency is the frequency at which systems tend to oscillate when disturbed. • Everything that can oscillate has a natural frequency, and most systems have more than one. Adding a steel nut greatly increases the inertia of a stretched rubber band, so the natural frequency decreases.

  18. 13.2 Changing the natural frequency • The natural frequency is proportional to the acceleration of a system. • Newton’s second law can be applied to see the relationship between acceleration and natural frequency.

  19. Key Question: What is resonance and why is it important? 13.3 Resonance and Energy *Students read Section 13.3 AFTER Investigation 13.3

  20. 13.3 Resonance and Energy • Harmonic motion involves both potential energy and kinetic energy. • Oscillators like a pendulum, or a mass on a spring, continually exchange energy back and forth between potential and kinetic.

  21. 13.3 Resonance • A good way to understand resonance is to think about three distinct parts of any interaction between a system and a force.

  22. 13.3 Energy, resonance and damping • Steady state is a balance between damping from friction and the strength of the applied force. • 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.

  23. Application: Quartz Crystals

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