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Investigating what happens when sound waves hit different types of surfaces.
Have you ever shouted into a big, empty gym and heard your own voice talk back to you a second later? It’s not a ghost—it’s science playing a game of catch with your voice!
Sound travels in waves, moving through the air until it hits something. When a sound wave hits a hard, flat surface like a tall cliff or a bathroom wall, it doesn't just stop. It bounces back! This 'bounce' is called reflection. If the surface is far enough away, you hear the sound again a moment later. We call this a reflected sound wave an echo. Think of it like a rubber ball: if you throw it at a concrete wall, it zooms right back to your hand.
Why do people love singing in the shower? 1. Shower walls are usually made of hard tile or glass. 2. When you sing, the sound waves hit the hard tile and reflect (bounce) immediately. 3. Because the room is small, the reflections happen so fast they blend together, making your voice sound louder and more powerful!
Quick Check
What is the scientific name for a sound wave that bounces off a surface and returns to your ears?
Answer
An echo (or a reflected sound wave).
Not every surface likes to play catch. Some materials act like a sponge for sound. When sound waves hit soft, fuzzy, or bumpy surfaces—like a thick rug, a pile of pillows, or a winter coat—the energy gets trapped inside the material. This is called absorption. Instead of bouncing back, the sound wave is 'soaked up' and turned into a tiny bit of heat energy. This is why a room full of people wearing heavy sweaters sounds much quieter than a room with bare floors.
Imagine a school hallway with a hard wood floor where footsteps sound like thunder. To fix this, the school could: 1. Cover the floor with a soft carpet to absorb the sound of shoes. 2. Hang fabric banners on the walls to soak up the sound of students talking. 3. By replacing reflecting surfaces with absorbing ones, the hallway becomes much quieter.
Quick Check
If you wanted to make a room very quiet, would you cover the walls in aluminum foil or thick foam cushions?
Answer
Thick foam cushions, because soft materials absorb sound waves.
Have you ever noticed that a new house sounds very 'echoey' before the furniture arrives? This is because there is nothing to stop the sound waves from bouncing off the hard walls and floors. Once you add a sofa, curtains, and a rug, the echoes disappear. Scientists who study how sound moves in a room are called acousticians. They use math to figure out exactly how much 'bounce' or 'soak' a room needs. For example, a movie theater needs lots of absorption so you only hear the speakers, not the echoes of the person eating popcorn behind you!
A musician wants to record a song without any echoes. 1. They use walls covered in wedge-shaped foam. The 'bumpy' shape helps trap sound waves from many angles. 2. They use heavy, double-paned glass to prevent sound from the street from entering. 3. By maximizing absorption, the microphone only picks up the 'dry' sound of the singer's voice.
Which of these materials is most likely to create an echo?
What happens to a sound wave when it is 'absorbed'?
An empty room is usually more echoey than a room full of furniture.
Review Tomorrow
In 24 hours, try to explain to a friend the difference between 'reflection' and 'absorption' using a rubber ball and a sponge as examples.
Practice Activity
Go into three different rooms (like a bathroom, a bedroom, and a closet). Clap your hands loudly in each and listen. Which one has the most 'bounce' and which one is the 'quietest'?