In physics, resonance is the tendency of a system to oscillate at maximum amplitude at certain frequencies, known as the system's resonance frequencies (or resonant frequencies). At these frequencies, even small periodic driving forces can produce large amplitude vibrations, because the system stores vibrational energy. It can be useful for a number of things: -Medicine: Shattering kidney stones, which eliminates the need for invasive surgery -Mining: Resonance can map out what the underground looks like, i.e landscape and there are other uses. These two are what popped into my mind.

everything has a natural frequency (resonant frequency). if a object is vibrated at its resonant frequency the amplitude of the oscillations will be large and chaotic. resonant frequency can be used to shatter a wine glass with the voice, the singer must sing at the same frequency as the resonant frequency of the glass to shatter it.

http://www.answerbag.com/q_view/281691 This is a Ninjitsu hand exercise set that is part of the "flutter stroke" or "quivering palm" substyle lessons. You will need some sort of container for fine sand with no rocks, gravel, or lumps (a pail that is 20 litres or 5 gallons will be enough ... or a deep firm box) and you will need a whole lot of small balloons. The sand container will need to be placed so it is elbow high at the upper edge, and it will need to be deep enough so when your finger tips touch the inside bottom, your elbow is just below the upper edge. The balloons will need to be SMALL / LARGE enough to be used to represent internal organs, from spleen size to liver size but no smaller or larger. For the sand - stand close to the sand container, make a firm "Knife hand" and strike vertically down into the sand. If you strike with a constant power and a constant firmness to your hand & arm, then the sand will stop your hand fairly soon and the depth of penetration will be minimal. If you strike with a vibrating flutter, by moving your hand back and forth just a little bit but very quickly (between 1/8" and 1/2" back and forth and at least 12 to 32 "flutters" per second) while you stab/strike your knife hand vertically downward, then the sand will "dance" from the vibration and will open up to allow your hand to slide easily and deeply into the sand ... until you can plunge your arm elbow deep and hit the bottom of the sand container with your finger tips. The balloons are to be filled with water and held in the horizontal, palm up, center of the hand. Raise and lower the hand slightly but quickly. As you move the water balloon up and down, it will be shape changed by the force of the motion. As you raise the balloon, it will become shorter and wider ... As you lower it, it will get taller and thinner. This will make waves within the balloon. You will need to understand the physics concept of resonance. As you move the balloon up and down, make slight changes to the amount of the height change and the speed of the "flutter" ... when you find the perfect distance and frequency for your flutters, you will notice that the waves vastly amplify themselves and suddenly rupture the balloon, splashing water all over. Then try hanging the balloon by a string, and hold your palm at the side of the balloon and flutter slap the balloon without "swinging" your arm ... just flutter your wrist and palm until the resonance ruptures the balloon. These exercises are then combined with techniques to teach ways to defend and attack within the "flutter stroke" or "quivering palm" substyle. This is how Ninjas blow up internal organs with what seem to be just a quick touch ... and how they can dive into a sand dune and disappear from sight, then swim away under the sand to escape.

This is a Lorentzian function, and this response is found in many physical situations involving resonant systems.