What are two types of fluids?

• A. Liquids and gaseous.
• B. Solids and liquids.
• C. Gels and foams.
• D. Vapors and plasmas.

Answer: (A)

Fluids are substances that can flow, lacking the rigid shape of a solid. The two most common types encountered in basic aviation maintenance concepts are liquids and gases. Liquids have a definite volume but take the shape of their container, and they flow when a force is applied. Gases have neither fixed shape nor fixed volume and will expand to fill the space available, also flowing easily. This combination of flowing behavior without a rigid form defines fluids. Other options mix materials that don’t fit this standard pairing: solids don’t flow, and gels or foams aren’t typically categorized as one of the two fluid types in this basic sense, while vapors and plasmas relate to gas-like states but aren’t the conventional two-fluid distinction used here.