Properties of Fluids

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Fluid Noun

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[floo-id]

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Fluid

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A material, such as a liquid or gas, that can flow and does not have a definite shape of its own.

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Example: This diagram shows that in liquids and gases (which are both fluids), particles are not in fixed positions and can move past each other, allowing the substance to flow.

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Pressure Noun

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[presh-er]

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Pressure

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The perpendicular component of a force exerted on a surface, divided by the total area over which the force is exerted.

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Example: This diagram shows that atmospheric pressure is lower at high altitudes (like a mountaintop) because there is less air pushing down from above.

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Pascal (Pa) Noun

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[pas-kal]

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Pascal (Pa)

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The SI unit of pressure, defined as one newton of force applied over an area of one square meter (1 N/m²).

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Example: This diagram shows that atmospheric pressure, measured in kilopascals (kPa), decreases with altitude because there are fewer air particles pressing down from above.

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Kilopascal (kPa) Noun

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[kil-o-pas-kal]

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Kilopascal (kPa)

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A multiple of the pascal unit for pressure, equal to 1000 pascals, often used for measuring atmospheric pressure.

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Example: This image shows a digital pressure gauge, a tool used to measure pressure in units like kilopascals (kPa), which is a key property of fluids.

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Kinetic-molecular theory Noun

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[ki-net-ik mo-lek-yuh-ler thee-uh-ree]

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Kinetic-molecular theory

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A scientific model that explains the properties of gases by describing gas particles as being in constant, random motion.

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Example: This diagram shows that as temperature increases, particles gain kinetic energy, moving from a fixed solid structure to a flowing liquid and then to a widely dispersed gas.

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Ideal gas Noun

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[ahy-deel gas]

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Ideal gas

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A hypothetical gas whose particles are assumed to take up no space and have no intermolecular attractive forces between them.

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Example: This diagram shows that an ideal gas consists of many particles moving randomly in straight lines inside a container until they collide with the container walls.

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Atmospheric pressure Noun

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[at-muh-sfer-ik presh-er]

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Atmospheric pressure

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The pressure exerted by the weight of the gases in the atmosphere on any surface within the atmosphere.

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Example: This diagram shows that atmospheric pressure is caused by the weight of a column of air being pulled down onto the Earth's surface by gravity.

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Boyle's Law Noun

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[boils law]

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Boyle's Law

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A gas law stating that the pressure and volume of a gas are inversely proportional at a constant temperature.

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Example: This image shows that as the volume of a container with gas decreases (piston pushed down), the pressure increases, and as the volume increases (piston pulled up), the pressure decreases.

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Charles's Law Noun

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[charlz law]

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Charles's Law

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A gas law stating that the volume of a gas is directly proportional to its Kelvin temperature at a constant pressure.

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Example: As the temperature of a gas increases from T1 to T2, its volume expands from V1 to V2, showing a direct relationship at constant pressure.

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Absolute zero Noun

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[ab-suh-loot zee-roh]

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Absolute zero

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The theoretical temperature at which a gas would have zero volume and all molecular motion ceases, corresponding to 0 Kelvin.

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Example: This diagram shows Absolute Zero (0 K) as the coldest temperature, comparing it to water's freezing and boiling points on three common temperature scales.