Since Mr.Tsien brought up his idea of physical mechanics,as a new field in engineering science,to public attention in the early 50's of the 20th century,innumerable application examples of physical mechanics approach in diverse fields have manifested its strong vitality increasingly.One of important aspects in applications of physical mechanics is to appropriately choose the microscopic quantity for the system in consideration and build a bridge to connect its relevant microscopic information to its desired macroscopic properties.We present two unique cases of using the physical mechanics approach to study colloidal stability.In the first case we measured the outcomes from artificially induced collisions at individual particle levels,by means of directly observing artificially induced collisions with the aid of optical tweezers.In the second case,by using T-matrix method,the microscopic quantity extinction cross section of the doublet can be accurately evaluated and therefore the measurement range and accuracy of the turbidity methodology for determining the CRC are greatly improved.
