Specific impulse
how efficiently a reaction mass engine creates thrust, which is often proportional to effective exhaust gas velocity
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.
Normalized specific impulse is the ratio of specific impulse to Earth's standard acceleration of gravity, g (in m/s2 or ft/s2). It is measured in seconds, and conveniently is the same number in both SI and imperial units. It can be understood as the time that one kilogram of fuel can produce one kilogram-force of thrust, which is equal to the time that one pound-mass of fuel can produce one pound-force of thrust.
Overview
Reaction engines, such as rockets and jet engines propel a vehicle by expelling mass in one direction, which pushes the vehicle in the other direction according to Newton's third law of motion. This expelled mass is called the reaction mass.
The public source identifies “Specific impulse” as how efficiently a reaction mass engine creates thrust, which is often proportional to effective exhaust gas velocity. This brief keeps that definition visible, then builds a research path around Specific, impulse and efficiently.
Why this record matters
A short description can identify a subject without explaining its stakes. For “Specific impulse”, the useful work is to connect “how efficiently a reaction mass engine creates thrust, which is often proportional to effective exhaust gas velocity” to the records capable of establishing context and consequence.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Aug 15, 2026. The linked authority identifier is Q51504. None of the 0 selected statements returned an explicit reference.
Overview language is designed for orientation and should not be treated as a substitute for the evidence cited beneath it. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “Specific impulse”, its source revision and the description used here.
- Expand the search: follow Specific impulse primary sources, Specific impulse archive and Specific research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “Specific impulse”?
- Which institution is responsible for the underlying evidence?
- What terminology or title could unlock a more precise catalogue search?
Search terms from this dossier
This entry incorporates text from “Specific impulse” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.