Sound Wave Basics

Sound Waves

• Sound waves are longitudinal waves composed of compressions and rarefactions.
• Vibrations that travel through a material medium cause these waves.

Compression

• Compressions occur when air particles are pushed closer together, creating regions of higher density and pressure.

Rarefaction

• Rarefactions happen when air particles are less crowded, resulting in regions of lower density and pressure.

Vibration

• Vibration is the complete back-and-forth motion of an object.

Characteristics of Sound Waves

• Travel in all directions: Sound waves travel away from their source.
• Travel Through Matter: Sound waves can travel through gases, liquids, and solids.
• Speed: They travel fastest in solids, slower in fluids and slowest in gases.
• Vacuum: Sound cannot travel through a vacuum.
• Representation: Sound waves cannot actually be seen, but they can be represented by spheres.

Sound Properties

• Differences in sounds depend on properties of the sound waves, accounting for why some sounds are loud, soft, high, or low.

How to Alter the Speed of Sound

• Density: Increasing the density of the medium (solid, liquid, or gas) increases the speed of sound.
• Temperature: Increasing the temperature of the medium (solid, liquid, or gas) increases the speed of sound.

Reflection of Sound Waves

• Sound waves bounce back when they strike a barrier in a process called reflection.

Echo

• An echo is a reflected sound wave.

Reflection in Gymnasiums

• Sound waves easily reflect off a gymnasium wall because gymnasiums typically have smooth, hard walls.

Echolocation

• Echolocation is the process of using reflected sound waves to locate objects; animals like bats, Beluga whales, and dolphins use echolocation.

Conditions for Echoes

• Distance: The distance between the sound source and reflecting surface must be at least 17 meters.
• Time Period: The time period between hearing the original sound and its echo should not be less than 0.1 seconds.

Measuring distance using Echos

• Echoes can measure distance or depth using the formula d = s x ½ t.

Echolocation Dependence

• Echolocation depends on how long it takes those sound waves to return to the ears.

Ultrasonography

• Ultrasonography is a medical procedure using echoes to see inside a patient’s body without surgery.

Sonar

• Sonar is a type of electronic echolocation.

Uses of Ultrasonography

• Medical Examination: Used to examine organs such as the kidneys and gallbladders and other organs.
• Prenatal Care: Used to check the development of an unborn baby.

Ultrasonic Waves vs. X-rays

• Detail: Ultrasonic waves give more detailed images due to their shorter wavelengths.
• Safety: Less harmful to human tissue than X-rays.

Resonance

• Resonance happens when a vibrating object causes a second object to vibrate because they have the same resonant frequency.

Sound Quality

• The difference has to do with its sound quality.

Distinguishing Sounds

• Instruments can seem different because they produce different sounds comprised of a few pitches.

Sound Travel

• Sound waves cannot travel through a vacuum.

Correct Answers:

• A laboratory experiment about the nature of sound; Sara observes a large, dark room with a strong echo and smooth, hard walls with few things in it (A).
• Sound travels fastest through glass (D).

Other Points

• For a man standing in front of a wall 360 m away who hears an echo after 2 seconds, the speed of sound is 360 m/s.
• If a man stands in front of a mountain, and a sound is heard after 2 seconds, the distance between the man and the mountain is 340 m.

Understanding Resonance

• Resonance occurs when a vibrating object near a second object causes the second object to vibrate.

Effectiveness of Ultrasonic Waves

• Ultrasonic waves are effective at producing images of objects inside the body because their short wavelengths can image small objects.

How the speed of sound changes dependent on temperature

• Molecules that have more motion (more energy and higher temperature) are able to transfer their vibrations more easily.
• This is less noticeable in liquids and solids because the particles are closer together.

Speed of Sound in Air Table Examples

• At 0°C, v = 331 + 0.6(0) = 331 m/s.
• At 20°C, v = 331 + 0.6(20) = 343 m/s.
• At 25°C, v = 331 + 0.6(25) = 346 m/s.
• At 100°C, v = 331 + 0.6(100) = 391 m/s.