Pressure

Key Stage 3

Meaning

Pressure is the force on a surface per unit area.

About Pressure

Pressure is measured in Pascals (Pa).

A large force on a small area causes a large pressure.

A small force on a large area causes a small pressure.

Equation

Pressure = Force/Area

\[P = \frac{F}{A}\] Where:

P = Pressure

F = Force

A = Area

Example Calculations

A hydraulic press is used to stamp metal. The press provides a force of 1000N over an area of 0.0002m2. Calculate the Pressure applied by the press.	A 25000N elephant stands on 4 feet. The area of each foot is 0.01m2. Calculate the pressure on one foot.	A person wearing stilettos rests their entire weight of 600N on one heel. The heel has an area of 0.0005m2
F = 1000N A = 0.0002m2 \[P = \tfrac{F}{A}\] \[P = \tfrac{1000}{0.0002}\] \[P = 5,000,000Pa\]	F = 25000N Area of 1 foot = 0.01m2 Area of 4 feet = 0.04m2 \[P = \tfrac{F}{A}\] \[P = \tfrac{25000}{0.04}\] \[P = 625,000Pa\]	F = 600N A = 0.0005m2 \[P = \tfrac{F}{A}\] \[P = \tfrac{600}{0.0005}\] \[P = 1,200,000Pa\]

Pressure in a Fluid

The force responsible for pressure in a fluid is the weight of all the particles above the object.

The pressure in a fluid decreases with height and increases with depth. The deeper into a fluid the greater the pressure.

Since pressure increases with depth then the bottom of an object will experience more pressure than the top of the object. This causes a force called upthrust.