How Does Sound Travel?

How Does Sound Travel?
Simple Explanation for Teens

We live in a world full of sounds and things that produce them. Thanks to advances in science and technology, we now know that it’s our brain and nervous system that help us make sense of these sounds.

We create sounds naturally—like when we talk or clap—and also by using technology, like speakers or musical instruments.

The branch of science that studies sound and how it works is called acoustics.

Let’s explore how sound travels—from where it starts to where it’s heard!

What is sound?

Let’s break down what sound is and where it comes from.
Sound is a form of energy that we perceive with our ears. It starts when something vibrates. Our ears can only hear sound if those vibrations reach them. That’s why sound needs a material medium—like air, water, or solids—to travel through.

The Difference Between Sound and Noise

Annoying or unpleasant sounds are called noise. In big cities, too much noise can cause noise pollution.

A sound becomes noise when it’s uncomfortable, disturbing, or gets in the way—like the sound of a drill, a siren, a dentist’s tool, or a squeaky door.

What Are Sound Sources?

A sound source is anything that produces sound. There are all kinds of sound sources around us.

The farther we move from a sound source, the quieter it seems. That’s because the energy reaching our ears decreases as the distance increases.

The Origin of Sound – Sound Sources: Examples for Teens

Sound sources can be natural or artificial, depending on where they come from.
Natural sound sources produce sounds from nature or from humans.

Examples of Natural and Artificial Sounds

Natural Sounds

• Animal sounds: 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: The wind blowing, rain falling, thunder rumbling, water from a waterfall or stream, or the crackling of wood in a fire.
• Human sounds: These include clapping, whistling, your heartbeat, and more. We can also use our vocal system—like our vocal cords, mouth, and larynx—to speak, sing, or shout.

Artificial Sounds

Artificial sounds are made by man-made objects. For example:

• Musical instruments (like a guitar)
• Machines (like an alarm clock)
• Transportation (like an airplane engine, car horn, or train whistle)
• Appliances (like a blender or a printer)
• And devices like speakers, which are designed specifically to produce sound.

How is Sound Produced?

Vibration as a Source of Sound

For sound to exist, there has to be vibration, and it needs to happen many times per second. Vibration is a fast and tiny “shaking” of the particles that make up an object. When the movement is slower, it’s called an oscillation.

Sound and Vibration – How Is Sound Created and Transmitted?

When an object vibrates, it creates sound.
For example:

• The movement of a guitar string
• Knocking on a door

These vibrations cause sound waves that travel through the air and reach our ears.

How Does Sound Travel? What Is a Sound Wave?

Vibrations move through the air as waves. These waves go from the vibrating object (like guitar strings) to our ears.

As the sound moves, it creates small changes in air pressure. Our ears are super sensitive to these pressure changes.
Once the sound waves reach our ears, they’re turned into electrical signals, which the brain understands as sound.

Sound Waves for Kids – How Does Sound Move?

A sound wave is the movement of vibrations traveling from one place to another.

But here’s the thing: our ears can’t pick up all the sound waves moving through the air.
These vibrations usually come from physical actions—like hitting a drum, strumming a string, or clapping.

Mediums that Sound Travels Through

Sound needs a medium to travel. That means it can move through:

• Air (gas)
• Water (liquid)
• Solids (like metal or wood)

If there’s no matter, there’s no sound—because sound can’t travel in a vacuum.

Sound in a Vacuum

What’s a vacuum?
A vacuum is a space where there’s no matter—not even air. It can be created in a sealed container with all the air removed.

Since there are no particles to vibrate in a vacuum, sound can’t travel there. Without a medium, the vibrations from a sound source can’t move—so no sound can be heard.

Fun Facts About Sound and Light

Differences Between Light and Sound

In space (like between the stars), there are no sounds—because there’s no air! That’s why, even if there were a giant explosion in space, you wouldn’t hear anything—you’d only see the light.

That’s a big difference between light and sound:

• Light doesn’t need a medium to travel. It can move through empty space at super high speeds.
• Sound needs something—air, water, or solids—to move through.

How Sound Propagates: The Speed of Sound

Which Medium Does Sound Travel Faster Through?

The speed of sound depends on the material it travels through. Sound waves move at different speeds depending on the medium. Sound travels faster through solids (like metal and wood), a bit slower through liquids, and slowest through gases (like air).

At What Speed Does Sound Travel?

• In air, sound travels at around 340 meters per second.
• In water, it moves faster—about 1,500 meters per second.
• In solids, it travels even faster. For example, in iron, sound can move at 5,000 meters per second!

The temperature of the material also affects how fast sound travels. When temperature rises, particles move faster, so vibrations (and sound) are transmitted more quickly.

Characteristics of Sound

We hear many different sounds every day. We often describe them with phrases like:

• “She sings with a high-pitched voice”
• “The TV is too loud”
• “My grandma speaks with a soft voice”

We can tell sounds apart based on three main characteristics: intensity, pitch, and timbre.

Intensity and Amplitude (Also Called Volume or Dynamics)

Some sounds are very loud, like an airplane engine, while others are soft, like the flutter of a bird’s wings.

Intensity (or volume) tells us how strong or weak a sound is. It depends on something called amplitude—how much energy a sound wave carries, or how strong the vibrations are.

• Intensity is measured in decibels (dB).
• A normal conversation is around 40–50 dB.
• A thunderclap can reach 110 dB!

Pitch or Tone of Sound

Pitch is what allows us to tell if a sound is high (like a whistle) or low (like a drum).

What makes one sound “sharper” or “deeper” than another?
It depends on how fast something is vibrating—this is called frequency.

• Frequency is measured in Hertz (Hz)—the number of vibrations per second.
• High-frequency sounds are high-pitched, and low-frequency sounds are low-pitched.

Infrasound and Ultrasound

Some sounds are too low or too high for humans to hear.

• Infrasounds are very low-frequency sounds. Animals like elephants and pigeons can hear them.
• Ultrasounds are very high-frequency sounds. Animals like dogs, dolphins, and bats can detect them.

We’ll talk more later about why animals can hear sounds that we can’t.

Timbre (Also Called Tone Color)

Timbre is what makes each sound unique, even if two sounds have the same pitch and volume.

For example, the same note played on a flute and a trumpet sounds different—that’s because of their timbre.

Timbre is also how we can tell different people’s voices apart, even if they’re speaking at the same volume and pitch.

How Does Sound Travel? Sound Reflection

When a sound wave hits something and bounces back, it changes direction. This is called acoustic reflection.

Echo vs. Reverberation

When sound reflects off surfaces, it can create:

• Echo – when the reflected sound is heard clearly and separately from the original.
• Reverberation – when the reflections blend together with the original sound, creating a kind of “echoey” effect.
• Resonance – when an object naturally vibrates at the same frequency as the sound, making the sound louder.

Acoustic reflection can amplify sound—in other words, make it louder.
An example of this is the stethoscope, which doctors use to listen to heart and lung sounds. Without it, those sounds would be too soft to hear. The stethoscope focuses the sound directly into the doctor’s ears.

Soundproofing Materials

Some materials don’t reflect sound—they absorb it and slowly reduce it. This is called sound absorption.

Materials like foam rubber, polystyrene, cardboard, wool, and even curtains, carpets, or acoustic panels, absorb sound instead of bouncing it back.

These materials are used as insulators in places where you want to keep sound from coming in or going out.
For example, in recording studios or rehearsal rooms, sound-absorbing materials help preserve sound quality and prevent echoes.

Difference Between Echo and Reverberation

An echo happens when sound reflects off a surface. It’s the repetition of a sound that bounces back after hitting something. In other words, an echo is a reflected sound wave.

It sounds like the original noise is being repeated, because the wave couldn’t pass through the obstacle and instead came back to you.
You might hear an echo when shouting near a wall, a tall mountain, or in a closed space with big, hard surfaces.

When many echoes overlap and bounce around continuously, we call that reverberation.

Sound in Humans and Animals

Humans have a lower hearing range than many animals.
There are sounds we can’t hear, but animals can.

But don’t worry—humans have other senses and abilities to understand the world around us!
These differences in hearing are not just about the brain, but also the shape, position, and size of the ears. That’s why some animals can detect infrasound and ultrasound.

Let’s explain what that means.

Categories of Sound Waves: Infrasonic and Ultrasonic

When objects vibrate, they produce sound waves—but not all of them are the same.
Sound waves are grouped into three categories depending on their frequency (how many vibrations happen each second):

Why Do Animals Hear Sounds That Humans Cannot?

When an object vibrates between 20 and 20,000 times per second, the waves are audible, meaning we can hear them.

If the vibrations are below 20 or above 20,000 times per second, humans can’t hear them—but some animals can. They have the ability to hear different frequencies of sound.

• Infrasonic waves (below 20 vibrations per second) are called low-frequency sounds.
  Elephants and whales use infrasound to communicate over long distances.
• Ultrasonic waves (above 20,000 vibrations per second) are called high-frequency sounds.

Examples of Sound Waves

• Dog whistles are ultrasonic—humans can’t hear them, but dogs can.
• The waves generated by earthquakes are infrasonic.
• Ultrasound, a medical technique based on ultrasonic waves, is often used to monitor the development of a baby during pregnancy.

What Is Echolocation and Which Animals Use It?

Some animals depend on echoes to survive.
They use a technique called echolocation to avoid obstacles, find their way, and hunt.

Echolocation is a system used by animals like bats and whales. They emit sounds that bounce off objects, and then they analyze the echo to understand their surroundings.

How Do Animals Hear?

Not all animals hear the same way. Each species has a different hearing ability.

Do all animals have ears?
No. For example, frogs don’t have visible ears, and birds don’t have external ears.

Animals with Super Hearing

• The owl has one of the most sensitive hearings—it can detect sounds from far away.
• The bat uses echolocation to hunt at night. It emits high-pitched sounds, listens for the echoes, and builds a mental map of the space around it.
• The shrew (a small mole-like animal) uses echolocation too.
• Dolphins communicate through the water using whistles and clicks:
  • Whistles: used for communication.
  • Clicks: extremely high-pitched (50,000–250,000 vibrations per second), used to detect the size, shape, and distance of objects underwater.

Other animals with amazing hearing include:

• 🐶 Dogs
• 🐱 Cats
• 🐘 Elephants
• 🕊️ Pigeons
• 🦋 Some species of moths