94 Sound-Mid

Sound Written by Robert N. Knight

What Is Sound? Can you describe sound? You might say that sound is something we hear with our ears. How does sound move from one place to another? How does sound get to our ears? How do our ears hear sound? This book will help you understand the answers to these and other questions about sound.

A thick blanket of air surrounds Earth. It is made up of particles so small, they cannot be seen. Sound moves through the particles in air. You hear it when it gets to your ears. Sound is a kind of energy. It has the ability to move things and do work. Sound makes the tiny particles of air vibrate. This means they move back and forth quickly.

Think about hitting a ball with a bat. This makes both of them vibrate. It makes the air around the bat and ball vibrate, too. The vibrations move through the air and away from them. The vibrations move farther and farther away. Wowser! Sound moves very fast. Sound near the ground can travel at 1,200 kilometers per hour (750 mph.) But it moves more slowly high above Earth, where air particles are more spread out.

How Do Waves Travel? Sound moves through air as waves of energy. These waves are like water waves you see in the ocean. But sound waves travel in every direction from the thing that makes the sound. All sound that you hear comes to you as a sound wave.

Sound waves are made when particles of air are pushed together and then spread out. Each wave has a regular pattern of particles that are squeezed together and then spread out. Sound waves made by different sounds look different. Let's look at loud and soft sounds.