Main branches of physics: statics, dynamics, fluid mechanics, analytical mechanics, kinematics, solid mechanics, material mechanics, composite mechanics, rheology, structural mechanics, elastic mechanics, plastic mechanics, explosive mechanics, magnetohydrodynamics, aerodynamics, rational mechanics, physical mechanics, celestial mechanics, biomechanics and computational mechanics. Fluid mechanics is a subject that studies the mechanical motion law of fluids (liquids and gases) and its application. The branch of mechanics that mainly studies the state of fluid itself and the interaction between fluid and solid wall, fluid and fluid, and fluid and other motion forms under the action of various forces. Composite mechanics is a new branch of solid mechanics, which studies the mechanical problems of multiphase solid materials composed of two or more materials with different properties on a macro scale. Structural mechanics is a branch of solid mechanics, which mainly studies the law of stress and force transfer of engineering structures and how to optimize structures. Elasticity, also known as elasticity theory, mainly studies the stress, strain and displacement of elastic body under the action of external factors such as external force or temperature change, so as to solve the strength and stiffness problems in structural or mechanical design. Explosion mechanics, a subject that studies the occurrence and development of explosion and the utilization and protection of its mechanical effects. It studies the process of sudden release or rapid transformation of energy such as chemical explosion, nuclear explosion, electric explosion, explosion induced by beam radiation (also known as radiation explosion) and high-speed collision, and the resulting effects such as strong shock wave (also known as shock wave), high-speed flow, large deformation and destruction, and throwing. Aerodynamics is a branch of mechanics, which mainly studies the mechanical characteristics, gas flow law and accompanying physical and chemical changes of objects in relative motion with gas. Biomechanics is a branch of biophysics, which uses mechanical principles and methods to quantitatively study mechanical problems in organisms. Its research ranges from the whole organism to systems and organs (including blood, body fluids, organs and bones), from bird flight, fish swimming, flagella and cilia movement to the transportation of plant body fluids. Computational mechanics is a new subject that uses modern electronic computers and various numerical methods to solve practical problems of mechanics according to mechanical theory.