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Definition of a BTU

Aviation Mechanic General (AMG) practice question 5 of 20 on Physics for Aviation. ACS element AM.I.J.K3 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONOne British thermal unit (BTU) is defined as the amount of heat required to change the temperature of

  1. A1 gram of water by 1 °C
  2. B1 lb of water by 1 °F
  3. C1 lb of water by 1 °C
Show the answer and explanation

Correct answer: B. 1 lb of water by 1 °F

  • A — incorrect This is the definition of the calorie, the metric heat unit, not the BTU.
  • B — correct The BTU is the English heat unit: the heat needed to change the temperature of 1 pound of water 1 degree Fahrenheit.
  • C — incorrect The BTU is defined using a Fahrenheit degree, not a Centigrade degree.

BACKGROUND

Two units are used to express quantities of heat energy: the calorie and the BTU. One calorie is the heat required to change the temperature of 1 gram of water 1 degree Centigrade. One BTU is the heat required to change the temperature of 1 lb of water 1 degree Fahrenheit. The calorie is seldom used in aviation maintenance, while the BTU is commonly used when discussing engine thermal efficiency and the heat content of fuel. One BTU of heat energy equals 778 ft-lb of work, and one pound of aviation gasoline contains 18,900 BTU.

STUDY TIP

Pair each heat unit with its measurement system: BTU goes with pounds and Fahrenheit, calorie goes with grams and Centigrade.

KEY POINTS

  • 1 BTU raises 1 lb of water 1 °F
  • 1 calorie raises 1 gram of water 1 °C
  • 1 BTU = 778 ft-lb of work

SOURCES

  • FAA-H-8083-30B ch05 "Heat Energy Units"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.