Strength of materials

Torsion pendulum

A threefold cord is not quickly broken.
— Holy Bible, Ecclesiastes, 4:12.

That same day Pharaoh gave this order to the slave drivers and the foremen in charge of the people: ‘You are no longer to supply the people with straw for making bricks; let them go and gather their own straw. But require them to make the same number of bricks as before; don’t reduce the quota.’
— Holy Bible (NIV), Exodus 5:6-8.

Egyptian and Greek buildings stand, for the most part, by their own weight and mass, one stone passively incumbent on another; but in the Gothic vaults and traceries there is a stiffness analogous to the bones of a limb, or fibres of a tree; an elastic tension and communication of force from part to part, and also a studious expression of this throughout every visible line of the building.
— John Ruskin (1819-1900)

A steel girder should be a hundred or a thousand times as strong as it is. Bridges should be built many times more cheaply. Aeroplanes should be immensely lighter than now appears possible. In each case, the atoms of which they are made flatter only to deceive.
— A. W. Haslett, Unsolved Problems of Science, London 1937.

In a memoir to the Academy in 1784, I provided the experimental laws for the torsion force on a twisted metal wire, and I showed that the restoring force was related to the angle of torsion, and to the fourth power of the wire’s diameter, divided by the length of the wire, and multiplied by a coefficient which depended on the nature of the metal, and which could be determined by experiment.

In the same memoir I showed that by using this force of torsion it is possible to measure accurately very small forces; for instance one ten-thousandth of a grain. In the same memoir I gave the first application of this theory, in finding the constant force attributed to adhesion in the formula that expresses the friction on the surface of a solid body moving through a fluid.

I present to the Academy today an electric balance built according to the same principles; it measures very exactly the state and electric force of a body, however small its charge …

FUNDAMENTAL LAW OF ELECTRICITY

The repulsive force between two small spheres charged with the same type of electricity is inversely proportional to the square of the distance between the centres of the two spheres.
— Charles Augustin de Coulomb (1736 – 1806), Mémoires sur l’électricité et le magnétisme, 1785.

Proposition VII: Among heavy prisms and cylinders of similar figure, there is one and only one which under the stress of its own weight lies just on the limit between breaking and not breaking: so that every larger one is unable to carry the load of its own weight and breaks; while every smaller one is able to withstand some additional force tending to break it.
— Galileo Galilei (1564 – 1642), Dialogues Concerning Two New Sciences, Second Day, Dover, 1954, 126.

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