One book is 5 mm thick, the thickness of six books is 5×6=30 mm, and the propulsion rate before cm and mm is 10, that is, 1 cm = 10 mm, so 30 mm =30÷ 10=3 cm.

Both centimeters and millimeters are units of length, and commonly used units of length are decimeter (dm), kilometer (km), meter (m), micron (micron), nanometer (nm) and so on. The international system of units has chosen seven independent quantities as basic quantities, the first being length. Its basic unit name is meter, the symbol is m, and centimeter is not an international unit.

The unit of length refers to the basic unit for measuring spatial distance, which is formulated by human beings to standardize the length. Length units play an important role in various fields.

The unit of measurement is the scale that people choose to measure a measurable size, and its value is determined by the definition of the unit. The physical standard with the highest accuracy reflects the numerical value given by the unit definition, which is called the measurement benchmark of the unit.

Easy Wrong point

Is centimeter an international unit? Chen Liqi discussed this topic with his colleagues in the teaching process. Because the middle school physics textbooks and college general physics textbooks in the hands of middle school physics teachers lack a systematic introduction to the knowledge of international unit system, there are great differences in the answers to this question.

Some colleagues think that centimeter is not an international unit, because it was taught by their teachers when they were studying in middle schools or universities, which makes me more eager to know the truth so as not to spread false information. Chen Liqi consulted relevant information and sorted out the following words for reference only.