What is thrust?

Thrust is the force described by Newton’s third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that system. The force acting on a surface in a direction perpendicular to or normal surface is called thrust. Force are measured using the International System of Units (SI) in newtons (symbol: N). It represents the amount required to accelerate one kilogram of mass by 1 meter per second squared.

Thrust Formula

The most general thrust equation is then given by:

F = (m dot * V)e - (m dot * V)0 + (pe - p0) * Ae . Normally, the magnitude of the pressure-area term is small relative to the m dot-V terms. The nozzle of a jet engine is usually designed so that the outlet pressure corresponds to the free jet.

How is thrust generated?

Thrust is most often generated by the reaction of accelerating a mass of gas. Since thrust is a force, it is a vector quantity with magnitude and direction. The engine runs on gas and accelerates the gas towards the rear of the machine; thrust is generated in the opposite direction by the accelerated gas. Thrust depends on the accelerated amount of gas and the difference in gas velocity through the engine.

Thrust Examples

One of the most common examples of thrust is one created by a rocket engine.

A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing force by ejecting mass rearward, following Newton’s third law.

The rocket moves forward using a thrust equal to the magnitude, but in the opposite direction, to the time rate of momentum change of the exhaust gas accelerated from the combustion chamber through the rocket engine nozzle. This is the exhaust velocity concerning the rocket, times the time-rate at which the mass is expelled, or expressed mathematically:

T = v\frac{dm}{dt}

Where T is the thrust (force), \frac{dm}{dt} is the change in the mass rate with time, and v is the velocity of the exhaust gases measured relative to the rocket.

When the rocket should be lifted from the ground, the initial thrust should be greater than the weight of the rocket.

Examples of the produced thrust of some rocket engines:

The most powerful engine made in the rocket industry is the F-1 which produces 1.5 million pounds (or 6.7MN) of thrust. It was in use till the late ’60s on a Saturn V rocket that had five F-1 engines on it.

The Raptor rocket engine, manufactured by Elon Musks SpaceX, has also been popular for the past few years. It will be in further use on Starship. This engine has twice as much thrust as the Merlin engines on the Falcon 9 and Falcon Heavy rockets. The Raptor engine produces 510,000lb of thrust. Raptor holds the record for the highest combustion chamber pressure ever reached by an operational rocket engine. It has 330 bar (33 MPa; 4,800 psi), surpassing the record held by the RD-701 rocket engine at 300 bar.

RS-25 is the main Space Shuttle engine is also in use by its successor, the Space Launch System (SLS). Each engine produces 1,859 kN (418,000lb) of thrust.

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