4.0 PRESSURE

Pressure is a concept that bridges simple calculations with the real‑world engineering of machines. These notes are designed for learners who may not have access to textbooks. Every idea is explained in depth, and many questions are provided so that you can practise until you master the topic. Let’s begin.

4.1 Definition of Pressure

Pressure is defined as the force acting normally (perpendicularly) per unit area. In everyday language, it tells us how concentrated a force is.

Mathematically:

P = F / A

where:

• P = pressure (measured in pascals, Pa)
• F = force applied normally (newtons, N)
• A = area over which the force acts (square metres, m²)

Key point: 1 pascal = 1 N/m². This means a force of 1 newton spread over 1 square metre produces a pressure of 1 pascal.

Pressure helps us understand why a sharp knife cuts easily (small area → large pressure) and why a tractor uses wide tyres (large area → small pressure, prevents sinking).

4.2 Pressure in Solids

For solids, pressure depends on two factors: the force applied and the area of contact.

• Maximum pressure is achieved when the same force acts on the smallest possible area.
  Examples: Sharp needles, knife blades, nails, pins. The tiny tip concentrates the force, producing high pressure that pierces materials.
• Minimum pres