Pressure & Forces (CIE IGCSE Physics)

What is pressure?

• Pressure is defined as

The force per unit area

• Pressure is measured in pascals (Pa)
  • 1 pascal is equivalent to 1 newton per metre squared
  • 1 Pa = 1 N/m²
• It can be calculated using the following pressure equation:

• Where:
  • p = pressure measured in pascals (Pa) or newtons per metre (N/m²)
  • F = force measured in newtons (N)
  • A = area measured in metres squared (m²)
• This equation can be rearranged with the help of a formula triangle:

A formula triangle can help rearrange the pressure equation

• For more information on how to use a formula triangle refer to the revision note on speed & velocity
• This equation tells us that:
  • If a force is spread over a large area it will result in a small pressure
  • If it is spread over a small area it will result in a large pressure

Examples of applications of pressure

• Example 1: Tractors
  • Tractors have large tyres
  • This spreads the weight (force) of the tractor over a large area
  • This reduces the pressure which prevents the heavy tractor from sinking into the mud

• Example 2: Drawing pins
• • Drawing pins have sharp pointed ends with a very small area
  • This concentrates the force, creating a large pressure over a small area
  • This allows the drawing pin to be pushed into a wall

Applying a force to a drawing pin

When you push a drawing pin, it goes into the surface (rather than your finger)

• Example 3: High heels
  • High heels have small, sharp points with a small area
  • This concentrates the weight (force), creating a large pressure over a small area
  • Flat shoes have a larger area which the weight (force) is spread over resulting in a lower pressure
  • This explains why high heels sink into soft surfaces more easily than flat shoes

The effect of surface area on pressure

High heels produce a higher pressure on the ground because of their smaller area, compared to flat shoes