Sound Intensity and Resonance 1986 world cup in mexico
Goal of the class To understand intensity, decibel level and resonance. Question of the Day: What are the dangers of resonance? Previous Answer: Sound with lower frequency than humans can hear f < 20 Hz Previous question: What is infrasonic sound?
Sound Intensity We discussed last time that sound waves spread out in a spherical pattern from the source. Intensity is given by the equation: I – the rate at which energy is transferred through an area.
Sound Intensity For a spherical wave the intensity decreases by the inverse square of the distance Show compression and rarefractions.
Decibel Level Show siren to drive off youths from shopping mall. Ask if they know any animals that can hear outside of this range. Elephants can hear lower frequencies, dogs higher. Mention dog whistles.
Decibel Level Scale is logarithmic 120 dB is the threshold of pain
Resonance Every object has a natural frequency, which is the frequency it would like to vibrate at. If a driving force has the same frequency as the objects natural frequency you can get large oscillations. This is called resonance. Pendulum example Talk about kids on swings
Dangers of Resonance
Homework Read chapter 12 – Section 2 Questions on P432 Q14, 17, 20, 22, 23