Matter & Energy · Depth 3 · Intermediate · 1 min read
Fluid Mechanics
How liquids and gases behave when they sit still and when they flow: pressure, buoyancy and the physics behind weather, pipes and flight.
What is it?
Fluid mechanics is the part of mechanics that deals with fluids. In physics, “fluid” means both liquids and gases: unlike solids, both of them flow.[1] That’s why water in a pipe and the air around a wing can be described with the same ideas.
A typical university course on fluids starts with density and pressure, then covers how pressure is measured, how hydraulic machines multiply force (Pascal’s principle), why things float (Archimedes’ principle and buoyancy), how fluids flow, Bernoulli’s equation, and finally viscosity and turbulence.[2]
Why it matters
- Weather. Falling air pressure goes hand in hand with dramatic weather such as hurricanes.[2]
- Flow and pressure. In a moving fluid, pressure and speed are linked: where the flow is faster, the pressure is lower. This is Bernoulli’s principle.[3]
- Flight. Around a wing, the air’s speed and pressure change from place to place, and adding up those pressures over the wing gives the lift force.[4]
Everyday examples
Real-life examples
Ears popping on a plane
The pressure change as a plane climbs is what makes your ears 'pop', the same effect divers feel underwater.[2]
Hot-air balloons and ships
Buoyancy, the upward push of a fluid, is what makes hot-air balloons rise and ships float.[2]
Measuring an aircraft's airspeed
A Pitot tube compares pressures in the flow to work out how fast the fluid is moving: Bernoulli's principle as a measuring tool.[3]
Go deeper
5 of 5 topics below this one are written so far. The rest are uncharted: on the map, but not yet written. The Atlas is growing.
- Bernoulli's PrincipleIn a flowing fluid, faster flow means lower pressure. It's a form of energy conservation, and one correct way to explain how wings make lift.
- AerodynamicsThe study of forces on objects moving through air, and the motion they cause. It explains what holds a plane up and what slows it down.2 branches
- BuoyancyWhy things float, sink or hover: the upward push of liquids and gases, Archimedes' principle, density, and how ships, balloons and divers use it.
Learn more
Short descriptions are our own summaries. The resources belong to, and are run by, their publishers.
- University Physics Volume 1 (free textbook) ↗
by OpenStax
A free, peer-reviewed university textbook covering mechanics, including forces, Newton’s laws and fluid mechanics.
- Beginner’s Guide to Aeronautics ↗
by NASA
NASA Glenn’s free, illustrated guide to how airplanes and rockets fly, from the four forces to engines and wind tunnels.
Evidence & sources
Supported by extensive evidence and broad scientific consensus.
Why this level? Pressure, buoyancy and Bernoulli's equation are foundational, long-established physics, backed here by a peer-reviewed university textbook and NASA.
This is a Knowledge Atlas editorial classification of the sources we could find, not a certificate of truth. How we evaluate knowledge
Sources
Based on 4 sources from 2 institutions: OpenStax, NASA.
Show all 4 sourcesHide the list
- ScholarlyOpenStax (Rice University)· Academic publisherUniversity Physics Volume 1, 14.1 Fluids, Density, and PressureOpened and checked against this page on 28 Sept 2026 · License: CC BY-NC-SA 4.0
- ScholarlyOpenStax (Rice University)· Academic publisherUniversity Physics Volume 1, Chapter 14: Fluid Mechanics (Introduction)Opened and checked against this page on 28 Sept 2026 · License: CC BY-NC-SA 4.0
- ScholarlyOpenStax (Rice University)· Academic publisherUniversity Physics Volume 1, 14.6 Bernoulli's EquationOpened and checked against this page on 28 Sept 2026 · License: CC BY-NC-SA 4.0
- National Aeronautics and Space Administration· Government agencyBernoulli and NewtonOpened and checked against this page on 28 Sept 2026