Part 1

Yesh! I know my english is improving, but i still want to write in english:)

P7 Constrained speed with length（Different from high school method: speed decomposition）

Note: Hypothesis the Point coordinates with (x,y).

P14 Deducing the formula of circular motion acceleration

Attention!!! Note: The vector of the vector function takes the unit vector.

Relative speed Calculation in Reference System

The relative speed of Reference System S’’ relative to Reference System S’ is u. The relative speed of Reference System S’relative to Reference System S is v. Figure： \(S''→（u）->S'→（v）->S\) The last step is vector summation.