Pressure in Fluids
Pressure increases with depth: P = ρgh.
About this topic
Pressure in a fluid at rest increases with depth: P = P₀ + ρgh, where ρ is density and h the depth. It acts equally in all directions at a given level and doesn't depend on the container's shape. Pressure itself is force per unit area, P = F/A, in pascals.
Divers feel about 1 extra atmosphere for every 10 m under water. Dams are thicker at the base because the pressure grows with depth, and water towers are built high to give tap water enough pressure to reach every house. Submarines must have strong hulls: at 1000 m the water pressure is about 100 atmospheres.
Worked example: at 20 m in a lake the extra pressure is ρgh = 1000 × 9.8 × 20 ≈ 196,000 Pa, almost 2 atmospheres, so the total is about 3 atmospheres. A diver rising too fast with air in the lungs risks injury because the gas expands as pressure drops.
The paradox that a narrow tall tube and a wide vessel with the same height of water give equal base pressure surprised early scientists. The weight of water is not what sets the pressure, only the depth. A common error is to use the total volume or width of the water, which is irrelevant. Remember also that gauge pressure leaves out the atmosphere, while absolute pressure includes it.
Key ideas
- Acts in all directions
- Independent of container shape
- Total pressure includes the atmosphere
Quick check
Use cases: where Pressure in Fluids helps
- Homework: review the key idea behind Pressure in Fluids before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Pressure in Fluids without notes.
- Visual learning: play with the interactive lab to see how Pressure in Fluids changes when you adjust its inputs.
- Teaching a friend: explain Pressure in Fluids in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Pressure in Fluids?
Pressure increases with depth: P = ρgh.
What will I learn in Pressure in Fluids?
Acts in all directions. Independent of container shape. Total pressure includes the atmosphere.
Is Pressure in Fluids part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Pressure in Fluids lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Pressure in Fluids?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.