Fluids, Density, Pressure & Buoyancy Lecture Notes

A set of vocabulary flashcards covering fundamental terms and principles related to fluids, density, pressure, buoyancy, Archimedes’ principle, Pascal’s principle, and their real-world applications.

Fluid

A substance (liquid or gas) that flows, takes the shape of its container, and continuously deforms under shear stress.

Liquid

A fluid with definite volume but no fixed shape; conforms to the container while resisting compression weakly.

Gas

A compressible fluid with neither fixed shape nor fixed volume, expanding to fill any container.

Density

Mass per unit volume of a substance; formula ρ = m ⁄ V, units kg / m³.

Mass Density

Alternate term for density; the ratio of an object’s mass to its volume.

Weight Density

Weight per unit volume of a fluid; D = ρ g, units N / m³ or lb / ft³.

Pressure

Force exerted per unit area on a surface, acting perpendicular to that surface; units Pascal (Pa).

Pascal (Pa)

SI unit of pressure equal to one newton per square meter (N/m²).

Buoyancy

The upward force a fluid exerts on an immersed object, opposing the object’s weight.

Buoyant Force

Magnitude of buoyancy; equal to the weight of fluid displaced by the object.

Archimedes’ Principle

States that an object submerged in a fluid experiences a buoyant force equal to the weight of the displaced fluid.

Pascal’s Principle (Pascal’s Law)

A change in pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and container walls.

Hydraulic System

A device using an enclosed fluid and Pascal’s principle to transmit or multiply force.

Hydraulic Lift

Machine with connected pistons of different areas; small input force on a small piston produces a larger output force on a large piston.

Hydraulic Brake

Vehicle braking system where pedal pressure is transmitted through fluid to actuate brake pads at each wheel.

Ballast Tank

Compartment in submarines or ships that can be filled with water or air to increase or decrease displacement and control buoyancy.

Specific Mass

Synonym for density; the mass of a substance divided by its volume.

Acceleration Due to Gravity (g)

The gravitational field strength near Earth’s surface, approximately 9.81 m/s².

Rho (ρ)

Greek symbol commonly used to represent density in fluid equations.

Upthrust

Another name for buoyant force—the upward push exerted by a fluid on an immersed object.

Pressure Due to a Liquid Column

Hydrostatic pressure calculated with P = ρ g h, where h is the depth below the fluid surface.

Shear Stress

A tangential force per unit area that causes fluids to flow and deform continuously.

Hydrostatic Weighing

Density-measuring technique using Archimedes’ principle by comparing an object’s weight in air to its apparent weight in water.

Gauge Pressure

Pressure measured relative to atmospheric pressure; excludes the atmospheric component.

Hull

The main body of a ship designed to displace water and generate buoyant force.

Dry Dock

Structure that employs buoyancy to raise and support ships out of water for maintenance or repair.

Trim Tab

Small, adjustable surface (often hydraulically actuated) used to balance and stabilize a boat by altering its pitch or roll.

Life Jacket

Personal flotation device that increases the wearer’s displacement and keeps them afloat by providing additional buoyancy.