Turning mass into momentum
A rocket accelerates by throwing mass in the opposite direction. The engine does not push on the air; it works in vacuum.
Propellant is converted into a high-temperature, high-pressure gas and accelerated through a nozzle. The exhaust carries momentum backward, and the vehicle receives an equal forward change in momentum.
Thrust tells us how hard the engine pushes. Specific impulse tells us how efficiently it uses propellant. A useful engine must match both to the mission rather than maximizing either in isolation.
Check your model01 question