"Frequency" is a very important concept in physics. Please tell us how the concept of frequency is defined and what the unit is. What is ultrasound?

The definition of frequency is: the number of times to complete periodic motion in unit time, with the unit of Hz and the symbol of Hz. Unit time usually refers to 1 sec.

It is a physical parameter that describes periodic motion. For example, mechanical vibration, back and forth, if repeated 1 0 times within1second, its frequency is 10 Hz; Another example is circular motion, which is also periodic and repeated. For example, the earth rotates once every 24 hours, so how many times does 1 second rotate? Answer: (hours need to be converted into seconds)1/24 * 3600 = 0.00001158 Hz, which is the frequency of the earth's rotation.

Learning frequency should be combined with another physical parameter-period. Period is defined as the time required for an object to complete a periodic motion. The previous example: mechanical vibration, if it is repeated 1 0 times within1s, the period is110 = 0. 1 s-that is, it takes 0.1s to complete once. Then, please think about it: how often does the earth rotate? What is the rotation period of the earth? What about the revolutionary period?

After careful understanding, it is not difficult to find the relationship between period and frequency. Please think for yourself.

Finally, I wish you progress in your study!