Water Pressure: Explore Below the Surface
Understand that pressure in a liquid at rest depends on depth and the density of the liquid (P = ρgh), acts equally in all directions, and does not change across the tank at the same depth.
Before you try
What if you moved the gauge sideways instead of down? Would the reading change at all?
Try it out
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What happened?
Move a control to see what changes and why.
The water is still and the temperature is fixed. Real pressure also shifts with temperature, and moving water behaves differently.
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Try these ideas
- Set the gauge to 5 m, then move it left, centre and right. Does the reading change?
- Switch from fresh water to sea water at the same depth and compare the readings.
- Turn on air pressure and see how much the atmosphere adds even at the surface.
Why it works
Every layer of liquid presses down on the layers below it, so the deeper you go, the more liquid is stacked above you and the bigger the push. Scientists write this as P = ρ × g × h: density times gravity times depth. Sea water is slightly denser than fresh water, so it presses a little harder at the same depth, and oil presses a little less.
In this simulator you fill a tank, lower a pressure gauge and slide it left or right. The reading climbs as the gauge goes down but stays exactly the same when it moves across, because only depth and density matter. Three holes in the wall spurt further the lower they are. The model treats the liquid as perfectly still and ignores the walls.
Check your understanding
Question 1 of 4
A gauge reads 49 kPa at 5 m in fresh water. You slide it sideways to the wall at the same depth. What does it read now?
Which gives the higher pressure at 4 m: fresh water (1000 kg/m³) or sea water (1025 kg/m³)?
Why does the lowest hole in the tank spurt the furthest?
A wide tank and a narrow tank are both filled to 3 m with water. Which has the higher pressure at the bottom?
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
For parents & teachers
- Ask why your ears hurt at the bottom of a swimming pool but not at the surface.
- Poke two holes at different heights in a plastic bottle of water and compare the jets.
- Discuss why dams are built thicker at the bottom than at the top.