page_title: Thrust
section_title: Examples
hierarchical_section_title: Thrust / Examples
context_page_description: Thrust is a force or a push. When a system pushes or accelerates mass in one direction, there is a thrust just as large in the opposite direction. In math and physics, this is described by Isaac Newton’s second and third laws. Thrust is used to describe how strongly an engine pushes. It can be used for many kinds of vehicles and engines such as rockets, motorboats, propellers, and jet engines.
  Thrust is measured in “pounds of thrust” in the U.S. and in newtons in the metric system. 4.45 newtons of thrust equals 1 pound of thrust. A pound of thrust is how much thrust it would take to keep a one-pound object unmoving against the force of gravity on earth.
context_section_description: An airplane makes forward thrust when air is pushed in the direction opposite to flight. The thrust is made by the spinning blades of a propeller. Thrust can also be made by a rotating fan pushing air out from the back of a jet engine. Another way is by ejecting hot gases from a rocket engine.
  Reverse thrust is the opposite of forward thrust. In this way air is pushed in the same way as the motion of the body. Reverse thrust can be used to help braking after landing. This can be done by redirecting the thrust in a turbofan or jet engine or by changing the blade angle of a propeller driven aircraft.
  Birds normally achieve thrust during flight by flapping their wings.
  A boat with a motor makes thrust or reverse thrust when the propellers are turned to push water backwards (or forwards). The thrust that this makes pushes the boat in the opposite direction than the water is being pushed.
  A rocket is pushed forward by a thrust force as large as the force the exhaust gas makes when going out of the rocket nozzle. The force the exhaust gas makes is called the exhaust velocity. The velocity is measured compared to the rocket. For vertical launch of a rocket to work, the starting thrust must be more force than the weight of the rocket.
caption: Forces on an aerofoil cross section