työntövoima

Työntövoima, or thrust, is the force that propels a vehicle in the direction of its motion. In physics and engineering, työntövoima is the reaction force produced when a propulsion system expels mass or accelerates the surrounding fluid. The net forward force depends on propulsion type and operating conditions.

Propulsion mechanisms fall mainly into reaction-based and momentum-based categories. Rocket and jet engines rely on reaction thrust: propellant or working fluid is expelled at high speed, pushing the vehicle forward. Propellers and fans generate thrust by accelerating air backward. Electric propulsion, such as ion thrusters, produces thrust by ejecting charged particles, typically with much higher efficiency for spacecraft than for aircraft.

Thrust is measured in newtons (N). In design practice, a simplified relation is F ≈ ṁ v_e, where ṁ is the mass flow rate and v_e is the exhaust velocity, with a small additional term for pressure differences at the nozzle exit. Thrust must exceed aerodynamic drag and weight to produce acceleration; the balance defines the vehicle’s performance. Specific impulse (Isp) relates to propellant efficiency rather than momentum directly.

Applications include aircraft, rockets, ships, submarines, and space probes. The concept rests on Newton’s third law and has developed from steam engines to modern chemical, electric, and nuclear propulsion, underpinning both everyday transportation and space exploration.