## Metadata - Author: [[J. E. Gordon]] - Full Title: Structures - Category: #books ## Highlights - The Roman army used to require that the officers in charge of military catapults should have a good musical ear, so that they could assess the tensions in the tendon ropes of these weapons when they were set up and tuned for action. ([Location 1643](https://readwise.io/to_kindle?action=open&asin=B009G1PHP2&location=1643)) - The larynx contains the ‘vocal cords’, which are strips or folds of tissue whose tensile stress can be varied by muscular tension so as to control the frequency with which they vibrate. Because the Young’s modulus of the vocal folds is rather low, large strains sometimes have to be applied to them in order to cause the necessary stresses; they are, in fact, stretched by a good 50 per cent when we want to achieve the top notes. Incidentally, the higher frequencies of the voices of women and children are caused, not by higher tensions in their vocal cords, but simply by the fact that the larynx is smaller and the vocal cords therefore shorter. ([Location 1649](https://readwise.io/to_kindle?action=open&asin=B009G1PHP2&location=1649)) - Plants and animals might be regarded to a considerable extent as so many systems of tubes and bladders whose function is to contain and to distribute various liquids and gases. ([Location 1658](https://readwise.io/to_kindle?action=open&asin=B009G1PHP2&location=1658)) - The earliest approximations to pressure-tight containers were the barrels of guns, and, historically, these were never very satisfactory and quite frequently failed. A list of the people who have been killed by the accidental bursting of guns, from King James II of Scotland downwards, would be long and impressive. Nevertheless, when gas lighting began to be installed in London, soon after 1800, the pipes had to be made by Birmingham gunsmiths, and in fact the earliest gas-pipes were actually made by welding musket-barrels end to end. ([Location 1664](https://readwise.io/to_kindle?action=open&asin=B009G1PHP2&location=1664)) - The skin of any pressure vessel really performs two functions. It has to contain the fluid by being watertight or gastight, and it has also to carry the stresses set up by the internal pressure. ([Location 1691](https://readwise.io/to_kindle?action=open&asin=B009G1PHP2&location=1691)) - When a hawk kills a bird in the air it does not usually do so by wounding it with its beak or talons – which would probably not penetrate the feathers. It kills by striking the bird in the back with its outstretched feet so as to impart a violent acceleration to the bird as a whole which has the effect of breaking its neck – very much as happens in judicial hanging. ([Location 1839](https://readwise.io/to_kindle?action=open&asin=B009G1PHP2&location=1839)) - The distortion of bows and chariot wheels under prolonged loading is due to what the engineer calls ‘creep’. In elementary Hookean elasticity we assume, for simplicity, that if a material will sustain a stress at all, it will sustain it indefinitely, and also that the strains in a solid do not change with time, so long as the stress remains constant. In real materials neither of these assumptions is strictly true; nearly every substance will continue to extend or creep under a constant load with the passage of time. ([Location 2088](https://readwise.io/to_kindle?action=open&asin=B009G1PHP2&location=2088)) - The amount by which materials creep, however, varies a great deal. Among technological materials, wood and rope and concrete all creep very considerably and the effect has to be allowed for. Creep in textiles is one reason why our clothes go out of shape and the knees of trousers get baggy; ([Location 2092](https://readwise.io/to_kindle?action=open&asin=B009G1PHP2&location=2092)) - Creep in any material causes the stress to be redistributed in a manner which is often beneficial, since the more highly stressed parts creep the most. This is why old shoes are more comfortable than new ones. Thus the strength of a joint may improve with age if the stress concentrations are diminished. ([Location 2100](https://readwise.io/to_kindle?action=open&asin=B009G1PHP2&location=2100)) - The strains to which present-day living membranes can be extended safely and repeatedly varies a good deal but may typically lie between 50 and 100 per cent. The safe strain under working conditions for ordinary engineering materials is generally less than 0-1 per cent, and so we might say that biological tissues need to work elastically at strains which are about a thousand times higher than those which ordinary technological solids can put up with. ([Location 2140](https://readwise.io/to_kindle?action=open&asin=B009G1PHP2&location=2140)) - Drops of liquid in air are of little use for biological purposes, because they soon fall to the ground; but droplets of one liquid floating within another liquid can continue to exist indefinitely and are of great importance both in biology and in technology. Systems of this kind are called ‘emulsions’ and are familiar in milk, in lubricants and in many kinds of paint. ([Location 2165](https://readwise.io/to_kindle?action=open&asin=B009G1PHP2&location=2165)) - another purpose of collagen fibres in flesh is to put up the work of fracture. This is a good thing for the animal, but it is inconvenient for the people who want to eat its flesh. In other words, it is collagen which makes meat tough. Nature, however, does not seem to be on the side of the vegetarians, because she has arranged, in her wisdom, that collagen should break down to gelatin – a substance of low strength when wet – at a somewhat lower temperature than that which elastin or muscle can withstand. The process of cooking meat therefore consists in converting most of the collagen fibres into gelatin (which is jelly or glue) by roasting or frying or boiling. ([Location 2394](https://readwise.io/to_kindle?action=open&asin=B009G1PHP2&location=2394))