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1. Propagation of Sound

2. Sound is a mechanical wave that arises from the back and forth motion of the particles in the medium through which the sound wave propagates. Sound

3. A sound wave is a longitudinal wave. Therefore, there are compression and rarefaction (stretched region) in its propagation. The displacement of one region of the slinky is parallel to its motion. Sound Propagation Movement of sound waves analogous to a slinky

4. Sound always come from a vibrating object. Source of Sound A ruler being flicked

5. Sound travels through any media: solid, liquid or gas Sound cannot propagate through a vacuum. Characteristics of sound: Pitch Loudness or intensity Properties of Sound

6. It corresponds to the frequency of a sound wave. It describes the highness or lowness of the sound. The higher the frequency of a sound wave, the higher the pitch Pitch

7. It corresponds to the amplitude of the wave. It is related to the energy being transferred by the wave. This quantity is measured in terms of decibels ( dB ). Loudness/ Intensity

8. Remember that pitch and intensity are not the same.

9. Difference between pitch and loudness as shown in a wave. Difference of Pitch and Intensity

10. Human ear can only hear a range of frequency. The range that can be heard by the human ear is called “audible frequency range”. The audible range is 20 Hz to 20 000 Hz Infrasonic - lower than 20 Hz Ultrasonic- higher than 20 000 Hz Can we hear everything?

11. infrasonic ultrasonic

12. Sound is a mechanical wave produced by the motion of the particles of the medium through which it moves. Sound can only be produced if there is vibration of particles The pitch of a sound is described by its frequency. The higher the frequency of a sound wave, the higher is the pitch. 1 2 3

13. The intensity of a sound is described by its amplitude. The greater the amplitude, the greater the intensity. It is measured in decibel (dB). Only frequency within the audible range can be perceived by the human ears. Below 20 Hz, it is called as infrasonic and anything beyond 20 000 Hz is called ultrasonic. 4 5

14. a barking dog produces a frequency of 25 Hz a soprano singer produces 750 Hz frequency a whale produces a sound with a frequency of 120 000 Hz when it whistles a giraffe produces 17 Hz sound frequency a speaker with a volume that ranges from 50 Hz to 400 Hz Write AR for audible range, IS for infrasonic and US for ultrasonic.

15. Why do we see lightning first before we hear thunder? Explain.