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# Why when hearing near the mouth of the thermos bottle does not contain water to hear o o

Have you experienced this? When your ear is near the mouth of an empty container such as a thermos, bottle, or cup, etc. will hear the o o. For what reason? Containers that contain nothing do not have a source of sound at all! This phenomenon in acoustics is called sound resonance. It is a resonance caused by the vibration of the sound source. For example, two objects pronounce the same frequency; if one object is not far from the other, only let one of them pronounce it, the other can follow the sound. That is the resonance phenomenon.

We can treat the air in those empty containers as an air column. An air column is also a pronounced object. When around an empty container with a sound of the appropriate frequency, the air column will produce sound resonance and make that sound intensify. After deep research, physicists have discovered: only need a sound with a wavelength of 4 times, or 3/4, 5/4 the length of the air column transmitted into the container can Cause sound resonance. The internal height of a normal hot water thermos is about 30 cm. It can be calculated that if there is sound with a wavelength of 120 cm, or 40 cm, 24 cm transmitted into the thermos, it is likely to cause sound resonance.

All around us is a world of sound, no moment without sound at all wavelengths: the sound of people and animals, the sound of wind and water flowing, the sound of cars and cars, even in the dead of night. The bar also has sounds from afar, and only they are relatively weak. We are not easy to hear. Among the many sounds, some types can excite resonant containers. The weak sound after causing the air column in the resonant container will be greatly increased. In general, there are always sounds of many types of wavelengths simultaneously producing resonance in them. That is the o we hear when we put our ears near the mouth of empty containers like a thermos and so on. The shorter the column of air, the shorter the wavelength of the sound, causing the resonance. Therefore, the sound of the o o coming from a small bottle would be more dazzling.

If the container has a cracked area, which causes the air column’s inherent completeness, the resonant sound will also be changed. Therefore, people often hear the sound of an empty thermos being checked for cracks or not.

James Smith
I used to look up at the sky when I was a child and wonder what's in those stars. Growing up, when I had the opportunity to contact the source of human knowledge, I had more knowledge about the universe, the natural world, and created laws. Being the founder of Wikiwap is where I can share my understanding of the world around me in a simple way that readers can access knowledge like a child. You and I are parts of the world; life will always be beautiful.