How Does Sound Travel?

We live surrounded by sounds and sources of sound. The brain and the nervous system are responsible for interpreting sounds. Moreover, we ourselves produce sounds both naturally and artificially. Let's learn about the sources that give rise to sounds.

How does Sound Travel? Simple Explanation for Children

Human beings reside in an environment filled with various sounds and sound-emitting entities. The progress made in the fields of science and technology has led to the understanding that it is our brain and nervous system that decipher these auditory stimuli. Additionally, we generate sounds both through natural means and through the utilization of technological devices. The scientific field dedicated to examining sounds and their properties is known as acoustics.

Discover how sound travels from where it originates to where it is heard

What is sound?

Let’s explain what sound is and how it originates. Sound is a form of energy that is perceived by our ears and originates from the vibration of an object. Our ears can perceive sound as long as the vibration of the object reaches them. Therefore, sound requires a material medium to travel and propagate.

Difference Between Sound and Noise

Annoying sounds that cause an unpleasant sensation in the ears are called noise. In large cities, excessive noise leads to sound pollution. A sound can become noise when it is unpleasant or when it interferes and bothers. For example, the sound of a drill, a siren, a dentist’s drill, or the high-pitched squeak of a door.

What are the sources of sound waves?

A sound source is any object or element that generates sound. There is a wide variety of sound sources. The farther we move away from a sound source, the less we hear the sounds it emits. This is because the amount of energy our ears pick up decreases as we move away from the source.

Depending on their origin, sound sources can be classified as either natural or artificial. Natural sound sources encompass sounds produced by nature itself, such as animals, wind, water, or geological phenomena. On the other hand, artificial sound sources are created by humans, such as musical instruments, machinery, or electronic devices.
What are the sources of sound waves?

The Origin of Sound – Sound Sources: Examples for Children

Sound sources can be natural or artificial depending on their origin. Natural sound sources produce sounds from nature and from humans.

Examples of Natural Sounds and Artificial Sounds

Natural Sounds

  • Animal sounds such as a cat’s meow, a dog’s bark, buzzing bees, a tiger’s roar, a cow’s moo, a hummingbird’s flutter, or a rooster’s crow.
  • Nature sounds like the sound of wind, rain, thunder, the falling water of a waterfall or stream, or the crackling of wood in a fire.
  • Human sounds: These are the sounds we make when clapping, whistling, the beating of our hearts, among others. We also have the ability to use our vocal apparatus, consisting of vocal cords, mouth, and larynx, which we use for speaking, singing, and shouting.

Artificial Sounds

Artificial sounds are those produced by objects. For example: From musical instruments (guitar), machines (alarm clock), means of transportation (airplane engine, car horn, train whistle), household appliances (blender, printer). The speaker, which is an instrument created to emit sounds.

How is Sound Produced?

Sound and Vibration: In order for sound to exist, there must be vibration, and it needs to occur numerous times per second. It is a rapid and minuscule "shaking" of the particles that compose an object. When the movement is slower, it is referred to as oscillation.
Sound and Vibration – How is Sound Generated by a Source Transmitted?

Vibration as a Source of Sound

In order for sound to exist, there must be vibration, and it needs to occur numerous times per second. It is a rapid and minuscule “shaking” of the particles that compose an object. When the movement is slower, it is referred to as oscillation.

Sound and Vibration – How is Sound Generated by a Source Transmitted?

The vibration of objects is responsible for generating sounds. Examples: the movement of guitar strings, a door being knocked.

How does Sound Travel? What is a sound wave?

Vibrations are transmitted through the air by waves that move from one point to another in the environment. Sound travels from the vibrating object (the strings) to the ears. We perceive moments of higher and lower air pressure. Our ears are very sensitive to pressure variations. Sound waves are converted into electrical signals that the brain later interprets as sound.

Propagation of Sound for Elementary School Children – What are Sound Waves?

A sound wave refers to the movement of vibrations that travel from one place to another. Human ears cannot capture all the waves that travel through the air. Vibrations are produced by mechanical actions, such as hitting a drum.

Propagation Mediums for Sound

Sound waves require a medium to travel. Sound not only travels through the air but also propagates in liquid, solid, and gaseous mediums. Vibrations can also travel through water or other solid materials, such as metal or wood. When there is no matter, there is no sound, as sound cannot be transmitted in a vacuum.

Sound in a Vacuum

What is a vacuum? Why can’t sound travel through a vacuum?

A vacuum is the absence of matter. A vacuum exists in a closed container without air or any other gas. In a vacuum, there is no matter or particles that can vibrate.

In a vacuum, there are no sounds because in the absence of a medium that can transmit the vibration from the sound source, sound cannot travel.

Fun Facts about Sound and Light for Kids

Differences Between Light and Sound

In intergalactic space, there are no sounds because there is no air. Sound does not propagate in a vacuum. If there were an explosion in space, we would only receive light. This is one of the differences between light and sound. Light travels millions of kilometers through empty space without needing a medium, but sound does not.

How does Sound Travel? Simple Explanation for Children
How Sound Propagates: The Speed of Sound

How Sound Propagates: The Speed of Sound

Which Medium Does Sound Travel Faster Through?

The speed of sound depends on the type of material it travels through. Sound waves propagate at different speeds depending on the medium. Sound travels faster through solids (such as metal and wood) and liquids than through gases (like air).

At What Speed Does Sound Travel? Through air, sound travels at a speed of 340 meters per second. On the other hand, in water, sound travels about 1500 meters in one second. In solid materials, sound propagates even faster. For example, in metals like iron, it can travel 5000 meters in one second.

The temperature of the material also affects the speed of sound propagation. As the temperature increases, the particles that make up the material move faster, and vibrations are transmitted more quickly.

How does Sound Travel? Simple Explanation for Children:  Characteristics of Sound

Characteristics of Sound

In our daily lives, we come across various sounds. We differentiate them using expressions such as “singing with a high-pitched voice,” “a loud TV,” or “the soft voice of a grandmother.” Sounds can be distinguished from one another based on their characteristics: intensity, pitch, and timbre.

Intensity and Amplitude (Dynamics)

There are intense sounds, like the one produced by an airplane engine, and less intense sounds, like the fluttering of a bird. Intensity is known as volume. It allows us to distinguish between weak and strong sounds. It depends on the amplitude, which is a property of waves that measures the amount of energy in a wave, in other words, the strength of vibration. Intensity is measured using a unit called decibel (dB). The volume or intensity of a conversation can reach 40-50 dB, while a thunderclap can reach 110 dB.

Sound and its Properties for Kids

Pitch or Tone of Sound

Infrasonic Waves (Infrasound) and Ultrasonic Waves (Ultrasound)

Pitch is the property that allows us to differentiate between low-pitched (bass) and high-pitched (treble) sounds. What makes a sound “thinner” or “thicker” than another?

It depends on the rhythm or speed of vibration, known as frequency. Frequency is the number of vibrations that occur in one second. It measures the number of waves that pass in one second, in other words, the rate at which an object vibrates. Sounds with higher frequencies are called high-pitched, while sounds with lower frequencies are called low-pitched.

Frequency is measured in a unit called Hertz (Hz). Very low-pitched sounds, inaudible to the human ear, are called infrasounds. Pigeons and elephants can perceive them. Very high-pitched sounds, inaudible to the human ear, are called ultrasounds. Dolphins, bats, and dogs can perceive them. We’ll explain later why animals can hear sounds that humans cannot.

Timbre (Tone Color)

Timbre is the property of sound that allows us to distinguish the source of the sound. Each sound source has its own timbre. If two different sound sources emit sounds with the same volume and pitch, they can be differentiated by their timbre. The same musical note sounds different if it comes from a flute or a trumpet. Thanks to timbre, we can recognize different people’s voices.

How Does Sound Travel? Sound Reflection

When a sound wave collides with an obstacle, it changes direction and reverses, it is said to bounce back.

Echo vs. Reverberation

This phenomenon is called acoustic reflection. The reflection of sound waves can produce phenomena such as echo, reverberation, and resonance. Acoustic reflection allows sound amplification, which means increasing its intensity. An example is the stethoscope used by doctors to listen to the sounds of the heart and lungs to check if they are normal. These sounds cannot be heard without this instrument because they are very weak. The stethoscope is used to concentrate the sounds in the doctor’s ears.

Echo vs. Reverberation
Echo vs. Reverberation

Soundproofing Materials

There are materials that, instead of reflecting sound, absorb it and gradually attenuate it. This is called sound absorption. Materials such as foam rubber, polystyrene, cardboard, wool (curtains, carpets, acoustic panels) do not allow sound to reflect but absorb it. They are used as insulation in places where you want to prevent noise from entering or exiting. For example, in recording studios or rehearsal rooms, these materials are used to preserve sound quality and avoid echoes.

Difference between Echo and Reverberation

An echo is the reflection of sound on a surface. It is a repetition of the sound produced by acoustic reflection on an object, therefore, an echo is a reflected sound wave. The sound “returns” and is heard as if it were being sent back because the waves cannot pass through the obstacle. For example, when you shout in front of a wall or a tall mountain, or in a closed environment with high walls.

Multiple echoes are called reverberation.

Sound in Humans and Animals

The auditory level of human beings is lower than that of animals. There are sounds that humans cannot hear, but animals can. But don’t worry! Humans have other abilities to interact with their surroundings. The differences are not only due to the auditory system but also to the arrangement and size of the ears. This is the case with infrasound and ultrasound. Let us explain a little further.

Categories of Sound Waves: Infrasonic and Ultrasonic

Objects vibrate in different ways. Sound waves are grouped into three categories according to their frequency (number of vibrations per second).

Sound in Humans and Animals: The  auditory level of human beings is lower than that of animals. There are sounds that humans cannot hear, but animals can. But don't worry! Humans have other abilities to interact with their surroundings. The differences are not only due to the auditory system but also to the arrangement and size of the ears. This is the case with infrasound and ultrasound. Let us explain a little further.
Sound in Humans and Animals

Why do animals hear sounds that humans cannot?

  • When an object vibrates between 20 and 20,000 times per second, the waves are audible and can be heard.
  • When they are below 20 or above 20,000 times per second, we cannot hear them. Animals can hear sounds of different frequencies.
  • When they vibrate less than 20 times, they are called infrasonic waves or low-frequency waves. Elephants and whales use infrasonic sounds to communicate.
  • When they exceed 20,000 times per second, they are called ultrasonic waves or very high-frequency waves.

Examples of Sound Waves

Dog whistles are ultrasonic, and the waves generated by earthquakes are infrasonic.

Ultrasound is a technique based on ultrasonic waves, widely used in medicine to monitor the development of the fetus during pregnancy.

What is echolocation and which animals use It?

Animal Echolocation

For some animals, echo is essential for their survival. They use this echolocation phenomenon to avoid colliding with obstacles. Echolocation is a mechanism used by some animals, such as whales and bats, to navigate and locate prey.

How do Animals Hear?

Echolocation: Friendly Definition for Kids and Students

  • Do all animals hear the same way? No. The ability to hear differs in each species.
  • Do all animals have ears? No. Frogs do not have ears, and birds do not have external ears.

Sound in Animals for Kids

Examples of Animals with Highly Developed Hearing

The owl is one of the animals with the most developed sense of hearing. It can hear a sound from many meters away. The bat hunts its prey at night. It emits short and high-pitched sounds that bounce off objects, receives their echoes, and creates a mental map of the surroundings. This allows it to fly in the darkness. The shrew (a type of mole) also possesses this ability. Dolphins use water as a medium for sound propagation. They emit sounds similar to whistles or clicks. They use whistles to communicate with each other. Clicks have a very high frequency (between 50,000 and 250,000 times per second). This is how they determine the size, shape, and distance of objects in the sea. Moths, dogs, cats, elephants, and pigeons have a great auditory capacity.

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