13.3 Resonance and Energy 1

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. 2

Chapter 13 Vocabulary Terms amplitude damping frequency harmonic motion hertz (Hz) natural frequency oscillator period periodic force periodic motion phase phase difference piezoelectric effect resonance stable equilibrium unstable equilibrium

Inv 13.3 Resonance and Energy Investigation Key Question: What is resonance and why is it important? 1. The restoring force pulls the pendulum toward the center (equilibrium). 2. The pendulum overshoots the center because of its inertia. 3. The restoring force pulls back toward the center, slowing and reversing the pendulum’s direction. 4. The pendulum overshoots the center again, because of inertia. 5. The cycle repeats, creating harmonic motion. 4

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.

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.

13.2 Resonance Resonance occurs when the frequency of a periodic force matches the natural frequency of a system in harmonic motion.

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.

Quartz Crystals The precise heartbeat of nearly all modern electronics is a tiny quartz crystal oscillating at its natural frequency. In 1880, Pierre Curie and his brother Jacques discovered that crystals could be made to oscillate by applying electricity to them. This is known as the piezoelectric effect.