1, there are 7 days in a week. People arrange their study, life, production and rest according to the "week", and it starts again and again every seven days. Students' schedules and employees' schedules are all in seven columns, as well as weekly meetings, weekly diaries, weekly salaries and weekends.

The Big Dipper consists of seven stars. People can look up at the "shifting star" of the seven stars every night, or they can find the Polaris hanging in the north forever according to the instructions of the Big Dipper.

There are seven basic colors in nature: red, orange, yellow, green, cyan, blue and purple, which are called "seven colors". White light passes through the prism and reflects red, orange, yellow, green, blue, blue and purple.

4. Mathematics is an abstraction of objective existence, and "7" is a special prime number in mathematics. A prime number cannot be expressed as the product of any other two integers except itself and 1. 1, 2, 3, 5, 7 are all prime numbers, but the reciprocal of 1 is 1, the reciprocal of 2 is 1.5, the reciprocal of 5 is 0.2, and the reciprocal of other numbers is ordinary decimal, but the reciprocal of 7 is infinite cycle decimal.

In music, "7" is the god of art in the material world. Duo, Lai, Mi, Fa, Suo and La constitute a wonderful music world. From the perspective of natural science, seven tones and eight degrees express the period of the vibration wavelength of an object; In art, 7 means natural rhyme and 7 means artistic auspiciousness.

6.PH value is a symbol used to measure the acid-base ratio of liquid in chemistry. When the PH value is greater than 7, the substance is alkaline, and the greater the PH value, the stronger the alkalinity; When the PH value is less than 7, the substance is acidic, and the smaller the PH value, the stronger the acidity. The substance is neutral only when the PH value is equal to 7.

There are seven continents in the world: Asia, Africa, Europe, Oceania, Antarctica, South America and North America. But many times, the uninhabited Antarctica will be removed, and South America and North America will be merged into "America", collectively known as "five continents".

8. 1999 On the eve of Macao's return to China, the song of the same name, adapted by the poet Wen Yiduo, was sung by Rong Yunlin, a little girl from Macao, and spread all over the country, causing people to sing. There are four words, five words, seven words and eight words in each sentence of ancient poetry, of which seven words are the majority, so there are seven laws and seven quatrains.