Glossary term
Thrust
A propulsive force generated by accelerating mass or interacting with a surrounding fluid.
Definition
quantityThrust is the propulsive force produced when a system accelerates mass or exchanges momentum with a surrounding fluid.
Thrust is the force that moves aircraft, rockets, propellers, fans, marine propulsors, and jet engines. It is governed by momentum change, pressure forces, mass flow, exit velocity, inlet conditions, and installation effects, and it must be evaluated together with drag, weight, lift, and mission profile.
For a simple steady control volume, net thrust can be understood from momentum balance. A propulsion system produces force by increasing the momentum flux of a working fluid and by pressure differences across inlet and exit planes. A simplified one-dimensional expression is:
where \dot{m} is mass flow rate, V_e is exit velocity, V_0 is incoming velocity, p_e is exit pressure, p_0 is ambient pressure, and A_e is exit area. The exact form depends on the chosen control volume and sign convention.
Engineering use
In aircraft, thrust must be compared with drag over speed, altitude, temperature, throttle setting, inlet distortion, and installation configuration. Static thrust on a test stand is not the same as installed thrust in flight. Jet engines, propellers, fans, and rockets also have different thrust characteristics because their mass flow, pressure ratio, and propulsive efficiency scale differently with speed and atmosphere.
In rockets, thrust is produced by carrying both propellant and oxidizer, so it does not require surrounding air. In propellers and marine systems, thrust depends strongly on blade geometry, advance ratio, inflow quality, cavitation, wake interaction, and rotational speed.
Common mistakes
A common mistake is quoting a single thrust value without altitude, Mach number, inlet condition, temperature, throttle setting, and installation losses. Another is comparing static thrust between propulsion systems that operate at very different flight speeds. A strong thrust review states operating point, control volume, mass flow, pressure terms, ambient condition, measurement method, uncertainty, and whether the value is gross, net, static, installed, or uninstalled thrust.