Learning About Sound Waves

As part of a sixth-grade science unit on waves, Mark McLean’s students learned about sound and light waves, including how these waves transfer different types of energy and how our bodies interpret these waves. For this project focused on sound waves, students designed and made their own instruments from recycled materials from their homes. As a minimum, the instrument had to make two different pitches (frequency) at various loudnesses (amplitude). Students had to demonstrate how their instrument works and provide a written explanation using the science terms they learned. Here’s a recap by two of Mr. McLean’s students. 

Types of Waves and How the Ear Hears Sounds 

There are two types of waves, transverse waves and longitudinal waves. Transverse waves have crests and troughs. Longitudinal waves have compressions and rarefactions. The top of a transverse wave is called a crest and the bottom is called a trough. Unlike a transverse wave, a longitudinal wave doesn’t have a bottom and a top to measure the wave. The wave is like a coil. Longitudinal waves have compressions and rarefactions. The compressions are the parts of a longitudinal wave that are pressed close together, and rarefactions are the ones that are not. Another difference is that transverse waves don’t require a medium, and longitudinal waves do require a medium. Remember that sound is simply vibrations that travel through a medium and are picked up by our ear and sent as nerve impulses to our brains. Our brain then uses these nerve impulses to determine what the sound is. 

There are different parts to the ear that do different jobs to allow humans to hear. The parts of the ear are the  ear canal, cochlea, auditory nerve, tiny bones (hammar, anvil, stirrup), and the eardrum. When sound waves travel through the ear canal, the sound waves go to the eardrum. When the sound waves enter the eardrum, the waves make the tiny bones vibrate. When the bones vibrate, they transfer the sound waves to the cochlea. The cochlea is filled with water and little hair-like nerves. The hair-like nerves send sound waves to the auditory nerve. The auditory nerve then sends a message to the brain telling the brain that that’s sound. 

— Corrinne Carter ’27 

Frequency, Amplitude and Resonance

A wave is just a disturbance of energy that moves from place to place. In a wave, energy is transferred, not matter. Sound waves are produced by vibrating objects. The objects vibrate because of energy. When energy is traveling, energy spreads out in all directions, making it harder to hear the sound in one specific place. 

Frequency and Pitch

With sound waves, if the frequency of the wave is higher, there will be a higher pitch noise coming from the wave. The lower the frequency of a wave, the lower the pitch. Pitch describes how humans hear the frequency of a sound. Different sound waves will have different pitches. Frequency is how fast a wave moves. If a wave moves slowly, there will be a low pitch sound. If the wave moves quickly, there will be a high pitch sound. The frequency is measured in hertz (Hz), where 1 Hz is equal to one cycle, or one wavelength.

Amplitude and Loudness 

One of the basic parts of a sound wave is amplitude, or volume, which determines how loud the sound is. Louder sounds have higher amplitudes and carry more energy. Quieter sounds have lower amplitudes and carry less energy. When people increase the volume of a sound, we are amplifying the sound. As the amplitude increases, the loudness increases. The amplitude of a wave is the height of the wave from the “baseline” or resting position. To simplify that sentence, amplitude is basically how tall or short a wave is. The volume of sounds depends on the height of the amplitude. Loudness is the intensity of a sound wave. The unit to measure loudness is the decibel (dB).

Resonance

Resonance is when you find an object with the same frequency as another object. For example, if someone has the same frequency voice as glass, they would be able to break the glass with their voice. They would break the glass by having the same frequency sound waves as the glass makes.  

In summary of all of our research and learning about waves, we created instruments that display how sound waves are made.  

— Bella Weeks ’27