More Than Meets the Ear

Illustration showing the Rarefactions and Compressions of a sound wave.

Sound is all around us, but few people realize what makes up a sound wave or what effect different mediums have on the waves. Sound is more interesting and complex than one would think. 

Transverse Waves are what most people imagine when they think of waves. These waves are the ones used when a string is plucked or there’s a ripple in water. However, sound waves are not Transverse, but Longitudinal Waves. The velocity of any wave can be calculated by multiplying the frequency by the wavelength. Wave velocity is the distance traveled by the wave per unit time, frequency is the speed of the sound’s vibration and determines the pitch (measured in Hz), and wavelength is the distance between two identical points on a wave. 

Waves have two different types of regions: Rarefactions are regions within the sound medium where molecules are more dispersed, and Compressions are regions where the molecules are clustered together. Mediums are anywhere that sound may pass through. A medium must be an area that is elastic, meaning things can be deformed and resort back to their original form. This is why sound cannot travel through outer space. Space isn’t an elastic medium, but instead a vacuum. The human ear can hear sound waves between 20-20,000 Hz. Sounds below 20 Hz are called Infrasonic and above 20,000 Hz are called Ultrasonic. Some animals can hear sounds above 20,000 and below 20 Hz. 

The speed of sound depends solely on the medium through which it passes. Every medium generates a different speed for sound. For example, the speed of sound is the highest in solids, followed by liquids, and finally the lowest in gasses. The speed of sound through air is 340 m/s or 760 mph. Some jets are capable of surpassing the speed of sound by almost 10 times. 

Sound waves tend to reflect or reverberate off smooth, hard surfaces, while they are usually absorbed by soft, irregular surfaces. The Law of Reflection states, “the angle of reflection is equal to the angle of incidence.” SONAR calculates how far away an object is by sending out a sound wave and then measuring the time it takes for the sound to return after being reflected. Similar to light, refraction of sound occurs when a wave continues through a medium and bends. 

Forced vibrations occur when an object is forced to vibrate at a certain frequency by an input force. Resonance is similar, but not the same. Resonance occurs when objects are forced to vibrate at their natural frequency. Sound waves are pressure waves, meaning they can exert a force on objects with the help of resonance. This is the reason why sound can shatter glass. Tuning forks will vibrate and resonate off each other if they’re at the same frequency. 

Interference has two types: Constructive and Destructive interference. Constructive interference is when two waves meet, combine, and increase each other’s amplitude. Destructive interference is when two waves meet, combine, and decrease each other’s amplitude. 

When a sound source travels it causes the frequency of the sound it creates to be higher in the direction the object is traveling and lower in the direction opposite to the traveling object. This is why ambulances sound much louder when they’re driving towards you than away from you. When an object travels faster than the speed of sound it produces a cone-shaped shock wave. When observers encounter this shock wave they hear a Sonic Boom or crack. Sonic Booms are not the sound of the sound barrier being broken, just the noise of sound waves overlapping and being compressed into a single conical shock wave. 

Sound is omnipresent, so learning about its intriguing anatomy helps us to understand our world. When it comes to the science of sounds, there is definitely more than meets the ear.

One thought on “More Than Meets the Ear

  1. Houston, This is a pretty amazing report that you have written ( as always).
    I was wondering which animals can hear sounds above 20,000 or below 20Hz? My guess would be dogs for one. I think maybe that’s why they howl when they hear the ambulance sirens. I have always thought that the sound hurts their ears.
    Thank you for teaching me something that I didn’t know. I thought that the sound of the sound barrier being broken was just that. Now I learn that it’s the noise of sound waves being compressed into a conical shockwave. Not that I can completely understand that. Nice learning new things at 80 years old. Actually there are plenty of things I need to learn. As they say you’re never too old to learn things.
    Keep the wonderful posts coming. I love them. I will show this to Papa tomorrow. He will enjoy it as much as I have.
    Love you ????, Gramsey

Leave a Reply