IB MYP 4-5 Physics- Pressure in liquids - Study Notes - New Syllabus
IB MYP 4-5 Physics-Pressure in liquids – Study Notes
Key Concepts
- Pressure in liquids
Pressure in Liquids
Pressure in Liquids
Liquids exert pressure due to the weight of the liquid above a certain point. This pressure increases with depth and acts equally in all directions at a given depth.
The formula for pressure in liquids is:
P = \(\rho g h\)
- \(\rho\) = density of the liquid (kg/m³)
- g = acceleration due to gravity (m/s²)
- h = depth below the surface (m)
- P = pressure (Pa)
Key Points:
- Pressure in liquids increases linearly with depth.
- Pressure depends on the density of the liquid and gravity, but not on the shape or volume of the container.
- At the same depth, pressure is the same in all directions (Pascal’s principle).
- Liquids are incompressible, so density is constant for most practical purposes.
Applications:
- Hydraulic presses and brakes (Pascal’s principle).
- Design of dams and submarines (pressure increases with depth).
- Measurement using manometers and barometers.
Example:
A diver is 20 m below the surface of seawater (\(\rho = 1025 \, \text{kg/m}^3\)). Calculate the pressure due to the water at this depth.
▶️ Answer/Explanation
Using \(P = \rho g h\)
\(P = 1025 \times 9.8 \times 20\)
\(P = 200,900 \, \text{Pa}\)
\(\boxed{P = 2.01 \times 10^5 \, \text{Pa}}\)
Example:
If a submarine descends from 50 m to 150 m in the ocean, calculate the increase in pressure on its hull. Assume seawater density \(\rho = 1025 \, \text{kg/m}^3\).
▶️ Answer/Explanation
Change in depth: \(h = 150 – 50 = 100 \, \text{m}\)
Using \(P = \rho g h\):
\(P = 1025 \times 9.8 \times 100\)
\(P = 1,004,500 \, \text{Pa}\)
\(\boxed{\Delta P = 1.00 \, \text{MPa}}\)