We can ask ourselves “What is sound really? How can we define it and is sound everything that human ear can hear?“. We define sound as longitudinal mechanical wave (sound needs medium to propagate) in frequency range from 20 Hz to 20 000 Hz. If sound can force an object to vibrate in its natural frequency, those vibrations will overlap, add up and make larger amplitude. We call this phenomenon resonance. It can make object to brake, and in this case it broke a glass. Besides the main characteristics of sound, this thesis will explained how and why resonance occurs and will describe experiments that show sound resonance that causes breaking of glass. Also, this thesis will represent the results connected to defining fundamental frequency of resonator and will explain how we can measure tuning fork frequency using oscilloscope and microphone. At the end of thesis there is a chapter that represents methodical elaboration of training unit called “Sound and ultrasound” that is a part of Croatian high school curriculum of physics of the third year.