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Pressure and density relationship

Remote Pilot (Part 107) practice question 9 of 25 on Weather / Effects on Performance. ACS element UA.III.B.K1a · difficulty: applied. Want to answer it in a timed quiz? Use the Remote Pilot (Part 107) practice mode.

Question bank updated 2026-09-22

QUESTIONThe temperature of a given volume of air is held constant while the pressure acting on it is doubled. What happens to the density of that air?

  1. AIt is halved
  2. BIt doubles
  3. CIt stays the same, since temperature is constant
Show the answer and explanation

Correct answer: B. It doubles

  • A — incorrect Density rises with pressure, not the reverse; halving would describe the effect of cutting the pressure in half.
  • B — correct The study guide states that density is directly proportional to pressure at a constant temperature: if the pressure is doubled, the density is doubled.
  • C — incorrect Holding temperature constant is the condition under which the direct proportion applies; it does not cancel the effect of pressure on density.

BACKGROUND

Air is a gas and can be compressed or expanded. When air is compressed, more air occupies a given volume; when the pressure is lowered, the air expands and the same volume holds less mass, so density falls. The study guide states that density is directly proportional to pressure: doubling the pressure doubles the density, and lowering the pressure lowers the density. This statement holds only at a constant temperature, because temperature has its own, inverse effect on density.

STUDY TIP

Keep the two rules separate: density is directly proportional to pressure (constant temperature) and inversely related to temperature (constant pressure).

KEY POINTS

  • Density is directly proportional to pressure at constant temperature.
  • Doubling the pressure doubles the density.
  • Temperature has a separate, inverse effect on density.

SOURCES

  • remote_pilot_study_guide.txt ch3b "Effects of Pressure on Density"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on 14 CFR part 107, 14 CFR part 89, and the FAA Remote Pilot – Small UAS Study Guide (FAA-G-8082-22). Regulations and handbooks are revised; confirm details against the current edition.