Slide 1
Deeper water supports more water above it
Pressure is force distributed over area. In still water, pressure increases with depth because deeper layers support more water above them.
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The extra pressure is approximately density times gravitational acceleration times depth. This simple relation assumes density changes little and the fluid is at rest; it describes a column without requiring a narrow container.
Slide 2
Equal depth gives equal pressure in connected resting fluid
At equal depths in the same connected resting fluid, pressures match. A wide lake and a narrow tube can create the same depth-related pressure.
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Container walls carry some of the forces in differently shaped vessels. The weight of all the water need not equal pressure times the bottom area, because wall forces also belong in the force balance.
Slide 3
Surface pressure adds to the water-depth contribution
Underwater pressure includes the pressure applied at the surface. Ocean measurements therefore distinguish total pressure from the increase caused by water depth.
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Seawater adds roughly one atmosphere for every ten metres of depth. Near ten metres, total pressure is therefore about two atmospheres when the surface air contributes about one atmosphere.
Slide 4
Pressure pushes perpendicular to each surface
A fluid at rest pushes on a small surface from every orientation. The force on that surface is perpendicular to it.
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A diver does not experience pressure only from above. Surrounding water transmits pressure around the body, while compressible gas spaces respond differently from tissues made largely of relatively incompressible material.
Slide 5
Greater pressure below an object produces buoyancy
The bottom of a submerged object experiences more pressure than its top. The resulting upward difference produces buoyancy.
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Pressure forces on the sides also contribute according to surface orientation. Adding all the fluid forces gives an upward force equal to the weight of the displaced fluid, connecting hydrostatic pressure to floating.