About this experiment
A deeper probe supports the weight of more liquid above it. Lower a pressure probe in a tank, compare liquids of different densities, and distinguish gauge pressure from absolute pressure. Changing pressure at the surface changes every absolute reading equally but leaves the depth gradient unchanged.
Learning goals
- Investigate how depth affects gauge pressure while controlling the other variables.
- Use the graph and numerical readings to test a prediction.
- Explain the physical assumptions and where this model stops applying.
How to use it
- 1Set density to 1000 kg/m³ and depth to 3 m. Check the gauge pressure is 29.43 kPa.
- 2Save the curve, increase density to 1200 kg/m³ and compare slopes.
- 3Keep depth fixed and change surface pressure. Which reading changes?
- 4Raise the probe to the surface. Explain why gauge pressure is zero but absolute pressure is not.
The model
Assumptions
- The liquid is at rest, has uniform density, and is incompressible. Gravity is 9.81 m/s².
- Depth is measured vertically below the surface. Tank width and liquid volume do not enter the pressure equation.
Try this in class
- Q1Why does a wider tank give the same pressure at the same depth?
- Q2At what water depth is gauge pressure approximately 98.1 kPa?
Frequently asked questions
Does pressure act only downward?
No. Static fluid pressure acts in all directions. The probe represents the local pressure at its depth.
Why are gauge and absolute pressure different?
Gauge pressure subtracts the pressure at the liquid surface. Absolute pressure includes that surface pressure.