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Difficulty: EasyProperties of Fluids

In a mechanical workshop, two identical syringes are sealed at the tip. One syringe is filled with atmospheric gas, and the other is filled with brake fluid. When a mechanic pushes down hard on both plungers, what physical difference between the two substances becomes obvious?

  1. A
    The liquid volume decreases greatly, while the gas volume stays nearly constant.
  2. B
    The volumes of both the gas and the liquid decrease by identical proportions.
  3. The gas volume decreases greatly, while the liquid volume stays nearly constant.Answer
  4. D
    The volumes of both substances remain completely unchanged regardless of the force.

Answer

The gas volume decreases greatly, while the liquid volume stays nearly constant.
Gases have widely spaced molecules and are highly compressible, meaning their volume decreases visibly under pressure. Liquids have closely packed molecules and are virtually incompressible, so their volume remains almost entirely constant even when force is applied.

Step-by-Step Solution

1
Identify the states of matter for the substances in the syringes.
The atmospheric gas is in a gaseous state, and the brake fluid is in a liquid state.
Determining the state of matter is the first step in predicting physical behavior under pressure.
2
Recall the compressibility properties of gases versus liquids.
Gases are highly compressible because their molecules are far apart. Liquids are generally considered incompressible because their molecules are closely packed.
This fundamental principle dictates how each fluid phase reacts to an applied force.
3
Apply this principle to the scenario of pushing the plungers.
The force easily compresses the gas, allowing its plunger to move down significantly. The force cannot significantly compress the liquid, so its plunger barely moves.
The physical difference in molecular spacing results in a highly visible difference in volume change.

Key Concept

Compressibility differences between fluid phases
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Topics

Properties of Fluids

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