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Unit 5, Chapter 13 CPO Science Foundations of Physics.

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Presentation on theme: "Unit 5, Chapter 13 CPO Science Foundations of Physics."— Presentation transcript:

1 Unit 5, Chapter 13 CPO Science Foundations of Physics

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

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 13.1 Harmonic motion Key Question: How do we describe the back and forth motion of a pendulum? *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 sound communications clocks nature


9 13.1 Amplitude Amplitude describes the size of a cycle.

10 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.

11 13.1 Linear Motion vs. Harmonic Motion Graphs


13 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.

14 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.

15 13.2 Why Things Oscillate Key Question: What kinds of systems oscillate? *Students read Section 13.2 AFTER Investigation 13.2

16 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.

17 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.

18 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).

19 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.

20 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.

21 13.3 Resonance and Energy Key Question: What is resonance and why is it important? *Students read Section 13.3 AFTER Investigation 13.3

22 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.

23 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.

24 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.

25 Application: Quartz Crystals

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