Pressure in a Liquid (CIE IGCSE Physics)
Revision Note
Author
LeanderExpertise
Physics
Pressure in Liquids
- A fluid is either a liquid or a gas
When an object is immersed in a fluid, the fluid will exert pressure, squeezing the object
- This pressure is exerted evenly across the whole surface of the fluid and in all directions
- The pressure exerted on objects in fluids creates forces against surfaces
- These forces act at 90 degrees (at right angles) to the surface
The pressure of a fluid on an object creates a force normal (at right angles) to the surface
- The pressure of a fluid on an object will increase with:
- Depth within the fluid
- Increased density of the fluid
Calculating Pressure in Liquids
EXTENDED
- The pressure is more accurately the difference in pressure at different depths h in a liquid, since the pressure changes with the depth
- The pressure due to a column of liquid can be calculated using the equation
Δp = ρgΔh
- Where:
- Δp = change in pressure in pascals (Pa)
- Where 1 Pa = 1 N/m2
- ρ = density of the liquid in kilograms per metre cubed (kg/m3)
- g = gravitational field strength on Earth in newtons per kilogram (N/kg)
- Δh = change in height of the column in metres (m)
- Δp = change in pressure in pascals (Pa)
- The force from the pressure is exerted evenly across the whole surface of an object in a liquid, and in all directions
The force from the pressure of objects in a liquid is exerted evenly across its whole surface
Worked example
Calculate the depth of water in a swimming pool where a pressure of 20 kPa is exerted. The density of water is 1000 kg/m3 and the gravitational field strength on Earth is 9.8 N/kg.
Exam Tip
This pressure equation will be given on your formula sheet, however, make sure you are comfortable with rearranging it for the variable required in the question!
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