Imagine throwing a stone into a calm body of water. The waves will ripple and expand indefinitely. This is similar to how sound waves move. A wave is any vibratory movement within a medium that carries energy from one point to another without direct contact. There are two types of waves – longitudinal and transverse. Sound waves are longitudinal waves.
Irregular repeating sound waves make noise while regular repeating sound waves produce music.
The vibration of air particles transports energy through the medium. This energy is moving in a wave-like pattern known as sound waves. Sound waves belong to longitudinal waves as vibrating particles move in the same direction where the wave is moving. Therefore, a longitudinal wave can travel in solid, liquid, and gas. On the other hand, transverse waves have particles vibrate at right angles where the wave is moving. They can only travel in solids and liquids, but no in gases.
Sound waves create compressions and rarefactions of the surrounding air. Compression is the region in the sound waves where air particles are closest to each other, whereas rarefaction is the exact opposite.
Sound waves have five distinct characteristics:
Wavelength – The distance in which its wavelength determines a sound wave repeat. One complete wave is made up of one compression and one rarefaction. A full sound wave is called a crest.
Amplitude – When waves pass through a medium, the air particles inside are temporarily displaced. The maximum displacement of particles is called amplitude. Amplitude describes how high or low the waves are. In simple terms, the amplitude is the sound’s volume. It is the basis of how loud or how soft sounds are.
Frequency – Frequency is the number of completed waves produced in a second. It is used to describe how fast waves are vibrating. When vibrations are fast (a high-frequency sound), high notes are created. When vibrations are slow (low-frequency sound), low notes are made.
Velocity – Velocity is the speed and direction at which sound travels. It depends on different factors, including humidity, density, and temperature. Sound generally travels faster at low humidity, low temperature, and high density. Therefore, velocity also determines how far can sound travel per second. Take note of this concept! We will use sound velocity to answer today’s question: Why could we hear faraway sounds better at night than during the day?
Why could we hear faraway sounds better at night than during the day?
We learned that sound travels faster in low temperatures. This means that sounds will travel faster and farther during the night when the air is colder. The refraction of sound waves changes the speed and direction (or the velocity) of waves when they pass from different mediums. Refraction is most evident when sound waves pass through a medium with varying properties.
Imagine you are at the swimming pool and your favorite jam is on the stereo. When you are out of the water, the music you hear is the actual sound of it. When you try to submerge your head underwater, you could listen to the sound, but it is different. Refraction is at play in this situation. This is also true during day and night.
Regions of air with different temperatures will have sound refracted to the cooler one before they could travel far. In the daytime, the temperature near the Earth’s surface is hotter than the air above. When sound waves propagate, say, your neighbor’s piano practices, the piano’s sound waves will be refracted towards the sky. In this case, you might not be able to hear the sound of it.
However, in the nighttime, the temperature near the Earth’s surface becomes cooler than the air above. This means, when your neighbor plays piano at night, the soundwaves will be refracted towards the ground, and you will hear it. You could also hear other sounds that you otherwise might not hear during the day – like your refrigerator’s engine, or the chimes of wind.
Did you notice that you can hear the sound of rushing air when it is about to rain? The same thing happens during summer and winter. You could listen to faraway sounds better in colder months than in hotter ones.