1. Definition
Containers that are open at the top and connected at the bottom are called communicating vessels.
Communicating vessels
Same liquid at rest → level surfaces; teapot & lock links.
Pressure (junior)Solid, liquid, atmospheric pressure and fluids.
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Communicating vessels
Communicating vessels: open tops, linked bottoms. Same liquid at rest → level free surfaces from equal bottom pressure (p = ρgh). Used in teapots, gauges, and locks — contrast with a closed hydraulic press.
Memory cue: open tops · linked bottoms · same liquid → level · ρ₁h₁ = ρ₂h₂ if different.
Key formulas
p = ρghsame liquid at rest → equal levels
How to use
- Read the Related knowledge map.
- Change fill, nudge an imbalance, then equalize.
- Link to teapots, gauges, and canal locks.
Read next
Related knowledge
Communicating vessels: open at the top, linked at the bottom. Same liquid at rest → free surfaces stay level.
2. Feature
With the same liquid and no flow, the free surfaces stay at the same horizontal level.
3. Why levels match
A thin liquid slab at the bottom feels equal pressure from both sides at rest. With p = ρgh and the same density, the column heights match — so the free surfaces are level.
p = ρghEqual pressures ⇒ equal h for the same liquid.
4. Applications
- Teapot: spout and body form communicating vessels.
- Boiler sight glass shows the water level inside.
- Water towers feed homes via level equilibration.
- Sink P-trap holds water against sewer gas.
- Road culverts drain both sides of a road.
- Canal locks (e.g. Three Gorges) raise or lower ships past a dam.
5. Pitfalls
- Equal levels need the same liquid at rest; different densities obey ρ₁h₁ = ρ₂h₂.
- Do not confuse with a hydraulic press: open leveling vs closed force multiplication.
Applications
- Teapots, canal locks, and water networks use communicating-vessel leveling.
- Spirit levels and boiler gauges are everyday applications.
FAQ
Why do the levels match?
At rest, bottom pressures match; same density implies equal heights from p = ρgh.
Is this the same as a hydraulic press?
No. Open vessels level out; a closed hydraulic press multiplies force by area ratio.
What if the liquids differ in density?
At rest you still get ρ₁h₁ = ρ₂h₂; surface heights need not match.
Must both sides hold the same liquid?
Same liquid → equal levels; different liquids obey ρ₁h₁ = ρ₂h₂.
How is this different from a hydraulic press?
Open vessels level out; a closed press multiplies force.