Sound is a longitudinal mechanical wave that travels through air, liquids, and solids as vibrations of molecules. It can have different frequencies, velocities, and wavelengths. Frequency describes how often the vibrations occur per second and determines whether a sound is high or low pitched. Sound travels at different speeds depending on the medium and temperature, with the speed increasing in denser materials. Humans can detect sounds between 20 Hz and 20,000 Hz, while some animals can hear sounds outside this range. Intensity and amplitude measure the energy of sound waves, with louder sounds having higher intensities and amplitudes.

1. Sound Waves

2. Characteristics
 It is a longitudinal wave.
 It is a mechanical wave. It travels through air,
solid, and liquid. It does not travel in a vacuum.

3. Note: When sound is transmitted through
electronic gadgets, sound is translated into
transverse wave.

4.  The vibration of molecules ( air, liquid, solid)
which carry the energy of sound.
 It has different frequencies, velocities and
wavelength.

5. Frequency – describes how often sound waves
vibrate per unit of time.
1 hertz = 1 vibration/second
1 Khz = 1000 vibrations/second
High frequency vs Low Frequency

6. High Frequency – sounds with high pitch
Low Frequency – sound with low pitch
The higher the frequency the shorter the wave
length, the lower the frequency the longer the
wave length

7. Low Frequency sounds can travel around
obstacles, and can travel long distances.
Examples
Low Frequency High Frequency
Hum of whales chirping of birds
Lion, elephants

8. Range of Frequency
1 – 19 Hz Sub sonic sounds, not audible to
humans
20 – 20,000 Hz – frequency of sounds which are
audible to humans
20,000+ Hz – super sonic sounds, not audible to
humans

9. Animals can detect sounds which are not
audible to humans.
Examples: dogs, cats, cat, fish

10. Intensity – measures the energy of sound. The
higher the energy, the higher the intensity.
Decibels – relative measure of sound intensity
dB Sound
10 dB soft whisper
20 dB rustling of leaves
65 dB human conversation
85 dB vacuum cleaner

11. 100 dB Rock Music
110 dB Jet Engine
150 dB Jet Engine at take-off
Frequent Exposure to 100 dB+ sounds can
destroy hearing.

12. Amplitude and Volume –the higher the
amplitude the louder the sound.
Amplifier – a device to increase volume of
sound.

13. Speed of Sound – refers to the distance covered
by sound per unit time.
Factors that effect velocity
 Speed is fastest in solid, then liquid, then gas.
 Elasticity of solid
 Density medium
 Temperature

14. Speed of Sound
S= 331.45 m/s + 0.61 m/s/C X T
Example:
What is Speed when temperature is 36 C?
What is speed when temperature is 16 C?

15. Frequency, Wave Length, Velocity
fv 

16. Laboratory Activity
Design or invent a technology that will help a
BLIND PERSON find his way in the busy streets
of Batangas City. (Use a bond paper)
- You must give a name to your technology
- Identify the parts
- Explain how it will work.