Ontario Grade 9 Science Class Practice Exam 2025 - Free Grade 9 Science Practice Questions and Study Guide

Sound waves are mechanical waves that require a medium to travel. This means they cannot propagate through a vacuum, or empty space, because there are no particles to transmit the vibration. Instead, sound waves travel through various media, including air, water, and solids.

In air, sound waves travel as longitudinal waves, where the air particles vibrate back and forth along the direction of the wave. In water, sound travels more efficiently due to the closer arrangement of molecules, which allows for faster transmission. Similarly, in solids, sound waves can also propagate due to tightly packed molecules that transmit vibrations effectively.

This ability to move through different types of media—gases, liquids, and solids—highlights the versatility of sound waves and is why the correct answer accurately describes their typical propagation method. Other options are limited in scope and do not encompass the full nature of sound wave propagation.