Module 2.2.1 Statics: forces, moments, stress and pressure

Statics studies bodies at rest (or moving at constant velocity) where all forces balance.

Knowledge levels

Sub-module	A	B1	B2 / B2L	B3
2.2.1 Statics	1	2	2	1

Content: forces, moments and couples, vectors; centre of gravity; stress, strain and elasticity (tension, compression, shear, torsion); properties of solids, fluids and gases; pressure and buoyancy in liquids (barometers).

Forces and vectors

• A force (newton, N) changes or tends to change the motion or shape of a body. 1 N accelerates 1 kg at 1 m/s².
• Weight = mass × g, with g ≈ 9.81 m/s². A 100 kg mass weighs about 981 N.
• Force is a vector: it has magnitude and direction. Mass, temperature and time are scalars.
• Vectors are added head-to-tail; two perpendicular forces combine by Pythagoras.
• Equilibrium: the resultant force is zero and the resultant moment is zero.

Worked example - resultant force

Two tugs pull an aircraft with 3 kN due north and 4 kN due east.

• Resultant = √(3² + 4²) = 5 kN
• Direction = tan⁻¹(3/4) ≈ 36.9° north of east