Understanding Sound: A Comprehensive Guide to Waves, Properties, and Applications
Chapter 13: Sound
Compression and Rarefaction
Sound waves create areas of varying pressure as they travel. High-pressure zones with tightly packed molecules are called compressions, while low-pressure zones with loosely packed molecules are called rarefactions.
Beats
Beats are fluctuations in loudness caused by the interference of sound waves with slightly different frequencies. The beat frequency is the difference between the frequencies of the two interfering waves.
Categories of Sound Waves
- Audible waves: Within the human hearing range (20 Hz to 20,000 Hz).
- Infrasonic waves: Frequencies below the audible range (e.g., earthquakes).
- Ultrasonic waves: Frequencies above the audible range (e.g., dog whistles).
Applications of Ultrasound
- Imaging small objects
- Medical diagnosis and treatment (e.g., observing babies in the womb, removing brain tumors)
- Measuring blood flow
- Ultrasonic ranging for cameras
Speed of Sound
Sound travels faster in solids than in liquids and gases due to the stronger interactions between molecules in solids. The speed of sound follows the order: Solids > Liquids > Gases.
Doppler Effect and Medical Uses
The Doppler effect is the change in frequency of sound waves reflected from a moving object. Doppler ultrasound is used in medicine to diagnose various conditions, including:
- Blood clots
- Valve problems
- Heart defects
- Blocked arteries
- Circulation issues
The Doppler effect is independent of distance; only the intensity of the sound changes as the source gets closer.
Shock Waves and Therapy
Shock waves are high-energy sound waves used to treat injured or painful tissues. Shockwave therapy promotes blood circulation, collagen production, and pain relief. It is commonly used for chronic pain conditions like plantar fasciitis, tendinopathy, and shoulder or hip pain.
Interference of Sound Waves
When sound waves from different sources interact, they create a new wave that is the sum of the individual waves. This phenomenon is called interference.
Shockwave Therapy Procedure
Shockwave therapy is a non-invasive procedure involving three phases:
- Locating the treatment area
- Applying gel for efficient wave transmission
- Applying shock waves with a handheld applicator
Typically, 3 to 5 sessions are required, with noticeable pain improvement often observed after the first session.
Preparation for Shockwave Therapy
No special preparation is needed as shockwave therapy is non-invasive and does not require anesthesia.
Standing Waves
Standing waves occur when two waves of the same frequency and amplitude traveling in opposite directions interfere with each other. They have points of zero amplitude (nodes) and maximum amplitude (antinodes). Examples include X-rays and mechanical waves.
Resonance
Resonance is the amplification of an object’s oscillations when it encounters matching vibrations from another object. Examples include:
- Sympathetic vibrations of a pendulum
- Resonance in radio and TV receivers
- Pushing a child on a swing
- Shattering glass with sound
Timbre
Timbre refers to the characteristic sound quality of a musical instrument, determined by the mixture of harmonics in the sound.
Pitch
Pitch is the perceived highness or lowness of a sound, primarily related to its frequency. It is a subjective experience that allows humans to categorize sounds on a scale.
The Ear
The ear consists of three parts:
- Outer ear: Includes the ear canal and eardrum.
- Middle ear: Contains bones that transmit sound to the inner ear.
- Inner ear: Processes sound and sends signals to the brain.