Sergey Alexeyevich Chaplygin (; 5 April 1869 – 8 October 1942) was a Russian and Soviet physicist, mathematician, and mechanical engineer. He is known for mathematical formulas such as Chaplygin's equation and for a hypothetical substance in cosmology called Chaplygin gas, named after him. He graduated in 1890 from Moscow University, and later became a professor. He taught mechanical engineering at Moscow Higher Courses for Women in 1901, and of applied mathematics at Moscow School of Technology, 1903. He was appointed Director of the courses in 1905. Leonid I. Sedov was one of his students. Chaplygin's theories were greatly inspired by N. Ye. Zhukovsky, who founded the Central Institute of Aerodynamics. His early research consisted of hydromechanics. His "Collected Works" in four volumes were published in 1948. Honours and awards Hero of Socialist Labour (1 February 1941) Two Orders of Lenin (1 February 1941 and 22 December 1933) Order of the Red Banner of Labour, twice (10 July 1927 and ?) Zhukovsky Prize (1925) Chaplygin was elected to the Russian Academy of Sciences (the Academy of Sciences of the USSR in 1925-1991) in 1924. The lunar crater Chaplygin and town Chaplygin are named in his honour. See also Chaplygin gas Chaplygin problem Chaplygin's equation Lamb–Chaplygin dipole Chaplygin sleigh Chaplygin's top External links 1869 births 1942 deaths People from Chaplygin Mathematicians from the Russian Empire Heroes of Socialist Labour Recipients of the Order of Lenin Full Members of the USSR Academy of Sciences Corresponding Members of the Russian Academy of Sciences (1917–1925) Moscow State University alumni Physicists from the Russian Empire Soviet mathematicians Soviet physicists 19th-century mathematicians from the Russian Empire 20th-century Russian mathematicians 20th-century Russian physicists Russian mechanical engineers Soviet mechanical engineers Engineers from the Russian Empire Central Aerohydrodynamic Institute employees