1. Sound

2. Speed of sound in solids, liquids, and gases Speed of sound in gas (air): 344 m/sec. Speed of sound in liquid (water): 1100 m/sec Speed of sound in solid (steel): 5000 m/sec Speed of sound wave dependenton strength of bonds between atoms. Why is helium so high and what is an example of this high speed

3. Temperature dependence of sound speed Speed dependent on temperature For liquids and gases speed increases for increasing temperature. One experiment to measure global warming is to measure speed of sound in oceans. Warmer oceans will result in slightly faster speed.

4. Speed of sound and sonic boom Plane moves through sound waves and creates a shock wave or “sonic boom”.

6. Intensity of sound An explosion or other sound producer such as a rock produces power. Units are Watts (W). Intensity (I) is a measure of the loudness of the sound a distance from the source. Units are W/m 2 The intensity decreases with the square of the distance from the source.

7. Intensity Intensity and Distance Example: At a distance of 10 m from source a sound has an intensity of 100 W/m2 What is intensity at a distance of 50 m? (10/50)2 = 1/25 = 0.04 I = 100 *0.04 = 4 W/m2

8. Examples of sound intensity For each example a person is 1 m from source. A Saturn rocket has a power 50,000,000 W compared to: 0.0000000000001 W for the threshold of hearing. Decibel scale- measures sound intensity, based on log scale (powers of 10)

10. Changes in intensity and dB. Question. How does a 80 dB compare to 70 db sound? 10 dB means 10 times louder. Question. How does a 80 dB compare to 60 db sound? 20 dB means 10 x 10 = 100 times louder. Question. How does a 80 dB compare to 50 db sound? 30 dB means 10 x 10 x 10 = 1000 times louder. Question: If a sound intensity is doubled from 1 W (120 dB) to 2 W what is the new dB? 123 dB (change in 3 dB).

11. Frequency and pitch Pitch is how high or low the sound is (not loud or soft) Pitch is dependent on vibrations per second or frequency Humans can hear a range between 20- 20000Hz Above 20000Hz is called ultrasonic – above our abilty to hear Timbre – refers to the quality of sound

12. Hearing Infrasonic –frequencies below 20Hz Ultrasonic –frequencies above 20000Hz So intensity is Amplitude Pitch is Frequency

13. Echoes and Reverberation Echo – reflection of sound. Reverberation – multiple reflection in a small area SONAR – SOund NAvigation and Ranging Uses an echo to determine distance

14. Doppler effect A change in frequency and pitch due to either motion of the observer or object

16. Resonance Adding energy at just the right frequency to get the amplitude to increase. Example: breaking a crystal glass