In a sound wave, the molecules in the medium vibrate back and forth from a ____ position.

In a sound wave, the molecules in the medium vibrate back and forth from a ____ position.

• A. fixed
• B. moving
• C. expanded
• D. stationary

Answer: (A)

The main idea is that particles in a sound wave vibrate around a fixed rest position. As the wave passes, each molecule moves back and forth about its equilibrium location, which stays in the same place in space even though the wave itself is moving through the medium. This is why the medium doesn’t travel with the wave; instead, the pattern of compressions and rarefactions moves, while individual molecules oscillate around a fixed point. If the reference position moved with the wave, or if the molecules didn’t move at all, the behavior wouldn’t match how sound waves propagate.

The main idea is that particles in a sound wave vibrate around a fixed rest position. As the wave passes, each molecule moves back and forth about its equilibrium location, which stays in the same place in space even though the wave itself is moving through the medium. This is why the medium doesn’t travel with the wave; instead, the pattern of compressions and rarefactions moves, while individual molecules oscillate around a fixed point. If the reference position moved with the wave, or if the molecules didn’t move at all, the behavior wouldn’t match how sound waves propagate.