Sound

Sound waves are very special motions of the molecules of the medium through which the wave moves. The medium could be air, water, or any other material. Sound travels at 343 meters per second in dry air an four times that fast in water!

Sound waves are special because the molecules of the medium travel in the same direction that the wave travels in. Such waves are called longitudinal. Even though the wave itself travels very fast, the air molecules do not move very far or very fast as the sound wave passes through the air.

Standing Sound Waves such as the one in this video have nodes that stay in the same place just like those for standing waves on strings. Notice how the molecules of air in the video move slowly left and right. Can you tell where the nodes are?

Sound Wavetrain is a video of a traveling sound wave passing through air. The wave travels to the right. Again notice that the air molecules only move a little bit back and forth , never moving far from their rest positions as the wave passes through.

Sound Pulse is a video of a pulse of sound moving through air. The air molecules are at rest until the wave hits them, then they move parallel to the direction that the sound wave travels in (to the right) and return to their resting positions.

Sound Wave