specific impulse
Sign in to savehow efficiently a reaction mass engine creates thrust, which is often proportional to effective exhaust gas velocity
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Specific impulse (usually abbreviated as Isp) is a physical quantity defined as the ratio of change in momentum (impulse) to the mass used, usually fuel. It typically uses units of metres per second (a SI unit) or feet per second (in imperial units). It is equivalent to thrust (a force, in newtons or pounds) per mass flow rate (in kg/s or lbm/s).
It serves as a measure of how efficiently an engine, such as a rocket or jet engine, generates thrust from propellant. Isp is the effective exhaust velocity used in the Tsiolkovsky rocket equation which calculates how much a vehicle's velocity can be changed with a given quantity of fuel.