2. Sound Waves Physics 1

3. Nature of Sound Sound is a longitudinal mechanical wave that travels through an elastic medium.

4. Speed of Sound Longitudinal mechanical waves (sound) have a speed dependent on elasticity factors and density factors.

5. Speed of Sound

6. For the speed of sound in air, where t c is in degrees Celsius

7. Intensity of Sound The sound intensity is the sound power that passes perpendicular through a surface per unit of surface area.

8. Intensity of Sound If a source emits sound uniformly in all directions, one can imagine the energy spreading out in a spherical pattern.

9. Intensity of Sound The smallest sound intensity audible to the human hearing is 1 x 10 -12 W/m 2. This intensity is called the threshold of hearing (I 0 ). Since human hearing has a wide range, the intensity of audible sounds is compared to the intensity at the threshold of hearing.

10. Intensity of Sound The sound intensity of a vacuum cleaner is around 1 x 10 -5 W/m 2. Comparing this intensity to the threshold of hearing,

11. Intensity of Sound Due to the large comparison, it is more appropriate to express this relative intensity (  ) in a logarithmic scale.

12. Intensity of Sound

13. Frequency of Sound The perceived frequency of an observer or pitch (f o ) of an emitted frequency of a sound source (f s ) depends on whether the observer or the source are in motion.

14. Frequency of Sound Source and Observer at rest

15. Frequency of Sound Moving Source

16. Frequency of Sound Moving Observer

17. Standing Waves L Fundamental, n = 1 1st Overtone, n = 2 2nd Overtone, n = 3 3rd Overtone, n = 4 All harmonics are possible for open pipes:

18. Standing Waves L Fundamental, n = 1 1st Overtone, n = 2 2nd Overtone, n = 3 3rd Overtone, n = 4 All harmonics are possible for open pipes:

19. Standing Waves Only the odd harmonics are allowed: Fundamental, n = 1 1st Overtone, n = 3 2nd Overtone, n = 5 3rd Overtone, n = 7 L

20. Standing Waves Only the odd harmonics are allowed: Fundamental, n = 1 1st Overtone, n = 3 2nd Overtone, n = 5 3rd Overtone, n = 7 L