GLOBAL KNOWLEDGE ARK

Reference library

Foundations

Explore concepts, laws, equations and methods, with clear explanations of their use and sources. Choose an area of study or find a specific entry.

More filters

Reference entries

Showing 61–90 of 1709 reference entries

Physics · MeasurementElectric current

Current measures charge crossing a chosen surface per unit time.

DefinitionPhysicsElectric field and force

An electric field assigns force per unit test charge.

DefinitionPhysicsMagnetic force on a moving charge

Magnetic force depends on charge motion relative to the field.

ModelPhysicsOhm's law and its domain

A linear current-voltage relation requires suitable conditions.

Empirical findingPhysicsFirst law of thermodynamics

Keep the heat and work sign convention explicit in an energy balance.

ModelPhysicsSecond law: isolated-system entropy

Apply entropy increase to the whole isolated system.

ModelPhysics · ChemistryIdeal-gas equation of state

A simple gas model relates pressure, amount, volume and temperature.

ModelPhysicsPhoton energy and frequency

One photon's energy is proportional to its frequency.

ModelPhysics · Mathematics & logicInvariant spacetime interval

Lorentz transformations preserve a combined space-time separation.

ModelPhysicsNewton's third law

Interaction forces act on different bodies in equal and opposite pairs.

ModelPhysicsAngular momentum and torque

Torque changes angular momentum about a specified origin.

ModelPhysicsHydrostatic pressure

Static fluid pressure rises with depth under gravity.

ModelPhysicsArchimedes' buoyancy principle

The hydrostatic upward force equals displaced-fluid weight.

ModelPhysicsMaxwell equations in free space

Four field equations connect electric and magnetic fields with charge and current.

ModelPhysicsSchrödinger time evolution

A quantum wavefunction evolves according to its Hamiltonian.

ModelPhysicsBorn position probability

A normalized wavefunction assigns probabilities to position intervals.

ModelPhysics · MeasurementElementary charge

The elementary charge has an exact SI numerical value.

DefinitionPhysics · MeasurementBoltzmann constant

The Boltzmann constant has an exact SI numerical value.

DefinitionMeasurement · Chemistry · PhysicsAvogadro constant

The mole is linked to a specified number of entities.

DefinitionMeasurement · PhysicsSI defining luminous efficacy

A specified frequency fixes the photometric SI reference.

DefinitionChemistryAtoms and elemental identity

The proton count of an atomic nucleus identifies its chemical element.

DefinitionChemistryIsotopes and mass number

Isotopes share a proton count but have different neutron counts.

DefinitionChemistryPeriodic organization of the elements

Atomic-number order reveals recurring patterns in electron structure and chemical properties.

ModelChemistryChemical bonds

Bonding describes interactions that bind atoms into molecules or extended structures.

DefinitionChemistry · MeasurementMole and amount of substance

The mole counts specified entities using the exact Avogadro constant.

DefinitionChemistryReaction stoichiometry

Balanced coefficients relate the amounts consumed and produced by a reaction.

MethodChemistryBalancing atoms and electric charge

A chemical equation must preserve each element's atom count and the total charge.

MethodChemistryDynamic chemical equilibrium

At equilibrium, opposing reactions continue without net composition change.

ModelChemistryBrønsted acids and bases

In the Brønsted description, an acid donates a proton and a base accepts it.

DefinitionChemistryGibbs energy and thermodynamic direction

Gibbs-energy change distinguishes thermodynamic favourability from reaction speed.

Model
ModelSource checked

Hydrostatic pressure

Physics

Static fluid pressure rises with depth under gravity.

Key knowledge

In a static fluid of uniform density under uniform gravity, pressure at vertical depth h below a reference level is p = p₀ + ρgh, where p₀ is pressure at that level.

Values and equations

p = p₀ + ρgh

p
Pressure at the lower level Pa
p₀
Pressure at the reference level Pa
ρ
Uniform fluid mass density kg m⁻³
g
Magnitude of uniform gravitational acceleration m s⁻²
h
Downward vertical depth from the reference level m

Conditions and scope

  • The fluid is at rest in the chosen inertial frame; ρ and g are constant over the depth considered.
  • h is a downward vertical depth; p₀ need not be atmospheric pressure.
  • Variable density, acceleration of the container and moving-fluid pressure require a different treatment.
Sources · 2

References

Sources retain their recorded scope. A source link alone does not establish verification of every statement.

  1. University Physics, volume 1: Fluids, Density, and PressureSamuel J. Ling, Jeff Sanny and William Moebs / OpenStax, Rice UniversityTextbook chapteropenstax.orgRead source
  2. Mechanical Properties of Fluids · Physics (2026–27 reprint)National Council of Educational Research and Training (NCERT)Textbook chapter · PDFncert.nic.inRead source

Evidence and review

OpenStax 14.1, equation 14.4 and static-fluid force balance; constant-density restriction contrasted with the atmosphere.

2026-10-10 · Uniform-density hydrostatic pressure difference only; no general flowing-fluid pressure law is asserted.

Foundational review

2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.

Sources from other places

Agreement within this scope

Static uniform-density fluid under constant gravity has downward pressure increase ρgh.

The upper reference pressure can be chosen generally; an open surface is the atmospheric special case.

Related reference entries

Explore relationships within this area of study and its connections to other areas.

Showing 1–4 of 4 relationships

Scientific relationships · 4 / 4

The relationship type describes the connection. Its linked statements, sources and conditions define the scope.

  1. Derived from
    Relationship sources · 1

    Balancing gravity and pressure forces on a static uniform-density fluid element gives the depth pressure difference.

  2. Derived from
    Relationship sources · 1

    The net hydrostatic pressure force equals displaced-fluid weight under the stated static-fluid and boundary assumptions.

  3. Related to
    Relationship sources · 1

    Linked statements

    • In a connected enclosed incompressible fluid at static equilibrium, an applied pressure increment is transmitted throughout without changing its value. For ideal pistons at equal height, the transmitted pressure increment gives F₂/F₁=A₂/A₁. Larger output force accompanies a smaller displacement; ideal hydraulic force multiplication does not create energy.

    The two records describe related physical or metrological models or distinctions; the present claim does not require every hypothesis or result in the linked record.

  4. Uses definition
    Relationship sources · 1

    Linked statements

    • Surface tension γ is force per unit effective contact-line length for a liquid interface. A thin soap film has two surfaces, so a movable wire of length ℓ feels 2γℓ. In a narrow circular vertical tube, static capillary height relative to a reservoir is approximately h=2γcosθ/(ρgr): wetting θ<π/2 raises the liquid, while θ>π/2 depresses it.

    This relation concerns the stated surface tension and capillary rise claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.

Entry detailsPermanent link to this entry ↗
Record identity
physics-hydrostatic-pressure
Revision
core.1
Structured reference record
Essential core · first collection · University core expansion