Vibration of an object is what produces sound waves. The vibrating object compresses air directly in front of it and moves in one direction. As the vibrating object moves in the opposite direction, the pressure on the air is decrease so that an expansion of air molecules occurs. One rarefaction compression and make up one longitudinal wave. The vibrating air molecules move back and forth parallel to the direction of motion of the wave receiving energy from adjacent molecules nearer the source and passing the energy to adjacent molecules farther from the source. Pitch is determined by the frequency of the tone that the ear receives. High notes are produced by an object that is vibrating a greater number of times per second than for a low note. Theloudness of a sound depends upon the subjective effect of intensity of sound waves on the ear. In general, more intense sounds are louder, but the ear does not respond similarly at all frequencies. Two tones of the same intensity but with different pitches may then appear to have different loudness.
How do sound waves travel through the air?
The vibrations of an object set particles in the surrounding medium in vibrational motion, which transports energy through the medium. The vibrations of each particles are best described as longitudinal, for a sound wave traveling through air.
the parts of the sound waves
In the diagram provided the white line represents the position of the medium when no wave is present. This medium could be thought as a rope fixed at one end a few feet above the ground and held by you at the other end. The yellow line in the diagram bellow stands for the position of the medium as a wave travels through it. The yellow line is a wave. If we consider the rope, which I mentioned before, this wave could be created by vertically shaking the end of the rope. Often when more than one wave is traveling, the continuous group of waves is often called a wave train. Since the waves are produced over and over again, with each wave requiring the same amount of time for it is creation we then say that the wave is periodic.