1. 1 PHYSICS Mr. BALDWIN WAVES 7-Feb-14 AIM: How does sound travel? DO NOW 1.How is sound generated (created)? 2.What is an echo? 3.What type of wave is a sound wave? Homework: In your own words, write a short ESSAY on the Doppler Effect (do not plagiarize) & WkShts 20.1 & 21.1

2. 2 Standing Wave A standing wave is generated in a pipe closed at one or both ends or on a string bounded on one or both ends. – ex. Organ pipe or guitar string A standing wave is generated by most musical instruments. Sound waves require the presence of matter in order to propagate. Light does not.

3. 3 Antinode: points that undergo maximum displacement Node: points of zero displacement What do you observe about the distance between nodes and antinodes? The distance between two consecutive nodes (or antinodes) in a standing wave is half the wavelength.

4. 4 Velocity of Sound Most sound are produced by vibrating objects, such as a cone of a loud speaker. Speed of sound depends on temperature CHECK…What is the speed of sound at 20 0 C? Speed of sound at standard temperature & pressure (STP - 20 0 C & 1atm) v sound = 343 m/s

5. Sound waves are described as pressure waves in a solid, liquid or gas Sounds waves are longitudinal waves – The molecules in their path moves back and forth in the same direction as that of the wave The velocity of sound also depends on the density of the medium. WHY? The denser the medium the faster it travels. – 1500 m/s in water; 5000 m/s in iron 5 Velocity of Sound

6. 6 Frequency of Sound Range of Audible Frequency of sound (sound that humans can hear): 20 Hz – 20 kHz. Infrasonic frequency range < 20 Hz – Sources includes earthquakes, thunder, volcanoes, heavy machinery Ultrasonic Frequency range > 20 kHz – Dogs & Bats hear in this range