Beats: When two sound waves of different frequency approach your ear, the alternating constructive and destructive interference causes the sound to be alternatively soft and loud - a phenomenon which is called "beating" or producing beats. The beat frequency is equal to the absolute value of the difference in frequency of the two waves.
Compression: In mechanics, compression is the application of balanced inward forces to different points a material or structure, that is, forces with no net sum or torque directed so as to reduce its size in one or more directions.
Forced Vibration: This is an example of resonance - when one object vibrating at the same natural frequency of a second object forces that second object into vibrational motion. The result of resonance is always a large vibration.
Infrasonic: relating to or denoting sound waves with a frequency below the lower limit of human audibility.
Natural Frequency: the frequency at which a system oscillates when not subjected to a continuous or repeated external force.
Pitch: the quality of a sound governed by the rate of vibrations producing it; the degree of highness or lowness of a tone.
Rarefaction: rarefaction, in the physics of sound, segment of one cycle of a longitudinal wave during its travel or motion, the other segment being compression.
Resonance: the reinforcement or prolongation of sound by reflection from a surface or by the synchronous vibration of a neighboring object.
Ultrasonic: involving sound waves with a frequency above the upper limit of human hearing.