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. Calculate the pressure due to the heel of the stiletto.
F = 1000N A = 0.0002m² \[P = \frac{F}{A}\] \[P = \frac{1000}{0.0002}\] \[P = 5,000,000Pa\]	F = 25000N Area of 1 foot = 0.01m² Area of 4 feet = 0.04m² \[P = \frac{F}{A}\] \[P = \frac{25000}{0.04}\] \[P = 625,000Pa\]	F = 600N A = 0.0005m² \[P = \frac{F}{A}\] \[P = \frac{600}{0.0005}\] \[P = 1,200,000Pa\]

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.

Key Stage 4

Meaning

Pressure is the force normal to a surface per unit area of that surface.

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 1100N over an area of 0.00023m². Calculate the Pressure applied by the press correct to two significant figures.	A 25000N elephant stands on 4 feet. The area of each foot is 0.012m². Calculate the pressure on one foot correct to two significant figures.	A person wearing stilettos rests their entire weight of 630N on one heel. The heel has an area of 0.00029m². Calculate the pressure due to the heel of the stiletto correct to two significant figures.
1. State the known quantities Force = 1100N Area = 0.00023m²	1. State the known quantities Force = 25000N/4 = 6250N per foot. Area = 0.012m²	1. State the known quantities Force = 630N Area = 0.00029m²
2. Substitute the numbers into the equation and solve. \[P = \frac{F}{A}\] \[P = \frac{1100}{0.00023}\] \[P = 4782608.696Pa\] \[P \approx 4800000Pa\]	2. Substitute the numbers into the equation and solve. \[P = \frac{F}{A}\] \[P = \frac{6250}{0.012}\] \[P = 520833.3Pa\] \[P \approx 520000Pa\]	2. Substitute the numbers into the equation and solve. \[P = \frac{F}{A}\] \[P = \frac{630}{0.00029}\] \[P = 2172413.793Pa\] \[P \approx 2200000Pa\]

Pressure in a Fluid

See Fluid Pressure for more detail.

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.

References

Pressure

Contents

Key Stage 3

Meaning

About Pressure

Equation

Example Calculations

Pressure in a Fluid

Key Stage 4

Meaning

About Pressure

Equation

Example Calculations

Pressure in a Fluid

References

AQA

Edexcel

OCR