Founder of “Physical Mechanics”

2015年09月28日

During his 20 years’ stay in the United States, Qian Xuesen spent most of his time studying the applied mechanics, made many famous achievements including the Kármán- Tsien formula, and participated in many projects in the missile development of the US military.

In summer, 1950, the Korean War broke out, stirring up a strong wave of anti-communist fever in the United States. Qian Xuesen was accused of being a member of the Communist Party, was forced to undergo inquest, detention and persecution, and even his daily academic study was affected as well.

Qian Xuesen had no choice but to change his “profession”, diverted to take on some theoretical study that had no direct relevance with the aerospace and spaceflight field. 

Those things did not beat him down. Instead, he put his whole heart and energy into the academic research and teaching activities.

Qian Xuesen placed his focus upon the higher and newer academic sectors, with opening up “Physical Mechanics” as one of his new achievements. The so-called physical mechanics does not refer to the classic mechanics concept in physics, but means a new branch of the applied mechanics that Qian Xuesen had studied for a long time.

Over years’ commitment to developing rockets, Qian Xuesen came to realize the fact that we must study and master how the macroscopic property of material or substance would change under some special and extreme conditions. For example, the nozzle throat temperature of a nuclear-powered rocket might rise up to 4000 K(3726.85℃), which would make it difficult for us to obtain the result through direct measurements as to the issue that how the thermodynamic property of substance would change under the abovementioned condition.

Qian Xuesen worked out a method to connect the following three parts together: the atomic and molecular structure theory for describing the microscopic properties of substances, quantum mechanics for describing microscopic behaviours of substances and the statistical mechanics linking up the microscopic and the macroscopic properties. Next, he incorporated the relatively well-established traditional applied mechanics on that basis and opened up a completely new discipline, determining the macro-mechanic properties of a substance in terms of its microscopic regularity. This is the origin of the concept of “Physical Mechanics”.    

In 1953, Qian Xuesen published the papers titled “Physical Mechanics-a New Field in Engineering Science”, officially proposed the concept of “Physical Mechanics” , and opened up a new field for high-temperature and high pressure liquid mechanics. 

Later on, Qian Xuesen set up the “Physical Mechanics” course in the California Institute of Technology, constantly enriched and deepened its content in the process of teaching and research, finally forming a bulky book named “Lecture Notes of Physical Mechanics”. You can see its English edition in the No.2 Exhibition Hall. To this day, the lecture notes are still an important reference material in the California Institute of Technology.

After his return to China, Qian Xuesen vigorously promoted and advanced the study of Physical Mechanics, imparting the cutting-edge knowledge of applied mechanics to Chinese mechanics researchers and students majoring in mechanics. In June of 1958, he stated in one of his manuscripts, “Physical Mechanics was brought up with a view to meeting the new technological needs, it was certainly a new discipline, but it was also a growing point between solid mechanics, liquid mechanics and physics and chemistry. Because it is a new thing, there are just a few relevant workers even in foreign countries with the advanced science and technology. This discipline is still in the bud in our nation, and its rapid growth necessitates strong and solid support, and only in this way can it meet the requirements of new technologies.” At the present time, these manuscripts are on display in the No.2 Exhibition Hall.    

After the University of Science and Technology of China was founded in 1958, Qian Xuesen set up the “Physical Mechanics” major and delivered lessons in person.

In 1964, to celebrate the meaningful occasion, Qian Xuesen took a photo with the graduates in physical mechanics major who were admitted to the University in 1959. As the founder of the Physical Mechanics, Qian Xuesen laid high expectations over the students who would become the vital force in physical mechanics study, and addressed to them with deep emotions, “we are the zero generation of the physical mechanics, and you are the true first generation!”