What is the principle of distinguishing whether watermelons are ripe by sound?

It is the hot summer season again, and the refreshing and delicious watermelon has become the "standard" in summer. Can you really judge the maturity of watermelons by slapping watermelons and listening to the sound? What is the principle of this seemingly simple way?

The researchers have conducted a study on "listening to sound to distinguish melons". The research shows that there is a scientific basis for slapping watermelons with their hands and judging the quality of watermelons by listening to sounds. The test principle of this method is that the propagation of sound waves in the medium is affected by the density and texture of the medium. therefore, the relationship between the sound waves obtained by slapping watermelons and the quality of watermelons can be found. In this way, without cutting the watermelon, we can analyze the sound waves obtained by slapping the watermelon and detect its maturity and internal quality.

Specifically, the structure of watermelon is divided into peel and pulp. In the process of watermelon ripening, the hardness and elastic modulus of the peel change, that is, the peel with ripe pulp is more elastic and will have a slight sense of rebound when slapped. In addition, under the action of cellulase, the internal cellulose is degraded, and the sugar content and structure of watermelon also change, so the percussion sound will be different naturally. Regarding the watermelon as an elastic multi-layer structure sphere, when people knock on the watermelon to make sound, the analysis of the sound wave signal can get the following results: when the immature fruit is flapping, its sound wave amplitude reaches the maximum, and then attenuates sharply, showing an irregular attenuation waveform. On the other hand, the maximum amplitude of suitable ripe fruit and over-ripe fruit appeared at a certain time after beating, and the waveforms were symmetrical and attenuated regularly. The embodiment of the sound wave is vibration and echo, so the sound is clearer when percussion is raw melon, and the sound is relatively dull is ripe melon.

To put it simply, the pulp density of raw watermelon is higher, the sound is crisp, while the pulp density of ripe watermelon is relatively low, and the vibration frequency of watermelon after being knocked is within the range that human ears can perceive and distinguish. Therefore, when buying watermelons, gently pat different watermelons, you can hear different sounds. When slapping watermelons makes a crisp "Dangdang" sound, it may be raw melons, the ones that make a muddy and heavy "bang-bang" sound should be ripe melons, and those who make "poof-poof" sounds may be over-ripe melons. In fact, in addition to tapping and asking about the sound, there are many ways to tell whether watermelons are good or bad. For example, the following "four views":

1. Look at the circle at the bottom of the watermelon. The smaller the better. On the contrary, the bigger the bottom circle, the thicker the skin and the worse it tastes.

2. Look at the watermelon head, which is the so-called melon stalk. Watermelons with curly stems are usually sweet

3. Look at the watermelon grain, the neat grain is better.

4. Look at the color of watermelon, watermelon had better pick turquoise, avoid picking fog white.