Fluids at Rest and in Motion

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Fluid Noun

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[floo-id]

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Fluid

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A substance, such as a liquid or gas, that has no fixed shape and yields easily to external pressure.

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Example: A fluid is a substance, like water, that has no fixed shape and can flow to take the shape of the container it is in.

Front

Pressure Noun

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[presh-er]

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Pressure

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The amount of force exerted per unit of area; in a fluid, it is transmitted in all directions.

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Example: The weight of the column of air above creates atmospheric pressure; there is less air and lower pressure at high altitudes than at sea level.

Front

Density Noun

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[den-si-tee]

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Density

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The mass of a substance contained within a specific unit of volume, representing its degree of compactness.

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Example: This image shows that a less dense pumice stone floats in water, while a more dense obsidian stone sinks, demonstrating the concept of density.

Front

Pascal's Principle Noun

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[pas-kals prin-suh-puhl]

Back

Pascal's Principle

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The principle stating that a change in pressure at any point in a confined fluid is transferred undiminished throughout the fluid.

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Example: Applying a force to a small piston in an enclosed fluid creates pressure that is transmitted to a larger piston, generating a larger output force.

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Hydraulic System Noun

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[hy-draw-lik sis-tuhm]

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Hydraulic System

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A machine that uses a confined fluid to transmit and multiply force, based on Pascal's principle.

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Example: Applying a small force (F1) to a small piston (Area A1) creates pressure in the fluid, which generates a larger output force (F2) on a larger piston (Area A2).

Front

Buoyant Force Noun

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[boi-uhnt fors]

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Buoyant Force

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The upward force that a fluid exerts on an object immersed in it, caused by the increase in pressure with depth.

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Example: This illustration shows a boat floating because the upward buoyant force from the water is balancing the downward force of the boat's weight.

Front

Archimedes' Principle Noun

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[ar-kuh-mee-deez prin-suh-puhl]

Back

Archimedes' Principle

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The principle that the buoyant force on an object is equal to the weight of the fluid displaced by the object.

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Example: An object submerged in water experiences an upward buoyant force equal to the weight of the water it displaces (5kg - 3kg = 2kg).

Front

Neutral Buoyancy Noun

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[noo-truhl boi-uhn-see]

Back

Neutral Buoyancy

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A state in which an object's weight is equal to the buoyant force, causing it to remain suspended in a fluid.

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Example: This diagram shows that an object experiences neutral buoyancy when the upward buoyant force (FB) is exactly equal to the downward force of gravity (Fg).

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Hydrothermal Vent Noun

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[hy-droh-thur-muhl vent]

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Hydrothermal Vent

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An opening in the seafloor from which geothermally heated water flows, often supporting unique ecosystems.

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Example: Cold, dense seawater sinks into the ocean floor, is heated by a magma chamber, and rises as hot, less-dense fluid through a vent.

Front

Bernoulli's Principle Noun

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[ber-noo-leez prin-suh-puhl]

Back

Bernoulli's Principle

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The principle stating that as the velocity of a fluid increases, the pressure exerted by that fluid decreases.

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Example: Air moves faster over the curved top of an airplane wing, creating lower pressure compared to the slower-moving air and higher pressure underneath, generating lift.