The Class 9 Science chapter on sound covers topics such as: Sound production and propagation Medium Wave and its types Characteristics of sound Audible frequency Reflection of sound and its laws Applications of reflection of sound

1. Sound

2. Properties of Sound
• Mechanical wave
• Needs a median to propagation.
• Can’t propagate in vacuum.
• Longitudinal wave
• Speed of sound in solid>liquid>gas
• Infra sonic(low frequency) are below 20hz humans can’t hear it
• Normal frequency 20hz-20000hz human ca hear this
• Ultra sonic( high frequency) humans cant hear this too

3. Production of sound
• Vibrating object.
• Particles in the surrounding vibrates
• Vibration reaches of ears.

4. Sound wave

5. Characteristics of sound wave
• Rarefaction: pressure and density are low
• Compression: pressure and density are high
• Frequency: number of wave produced in a second
• Time period: time required to produce one oscillation
• Amplitude: distance from crest/trough to the medium line
• Wavelength: distance between two waves

6. Characteristics of Sound
• When frequency increases pitch increases.
• When amplitude increases loudness increases.
• Quality or timbre it is a characteristic which distinguishes two sound
with same frequency and amplitude.

7. Laws of reflections of sound
• The angle of reflection is always equal to the angle of incidence.
• The reflected sound, the incident sound, and the normal sound
belong in the same plane.

8. Uses of multiple reflection of sound
• Statoscope
• Musical instruments
• Megaphones
• Auditorium ceiling

9. Uses of Ultrasonic sounds
• They are used in medical field for diagnosis and treatment of internal
illnesses of the human body.
• Using ultrasound, kidney stones can be broken into small grains
which later on get flushed out through the urine.
• Ultrasonography is used to examine the fetus during pregnancy.
• Ultrasound is also used in heart checks (ECG).
• Industrially, ultrasonic sounds are useful in examining metals for
defects like cracks etc. and for cleaning machine parts.