Extremely high frequencies of 100 to 500 kHz can cause strong physical and chemical reactions. They can force water and oil to emulsify, dust to collect, and gases held in liquids or molten metals to bubble out. They destroy certain types of bacteria. The intensity of a sound has nothing to do with its pitch. A high tone can be either loud or soft, and so can a low tone.
Intensity depends upon the strength, or amplitude, of the vibrations producing the sound.
A piano string, for example, vibrates gently if the key is struck softly. The string swings back and forth in a narrow arc, and the tone it sends out is soft. If the key is struck forcefully, however, the string swings back and forth in a wider arc. The stronger vibration then produces a louder tone. The explanation of this is that a vibration of greater amplitude compresses the molecules of the air more forcefully and gives them greater energy.