Any of a class of
Jets rely on the third of {{link=Newton's laws of motion">Newton's laws of motion (action and reaction are equal and opposite). The first jet-powered airplane was introduced in 1939 in Germany. The jet engine, consisting of a gas-turbine system, significantly simplified propulsion and enabled substantial increases in aircraft speed, size, and operating altitudes. Modern types of jet engines include turbojet s, turbofans, turboprop s, turboshafts, and ramjet s. See airplane . See also drag ; gasoline engine ; lift .