An experiment to demonstrate terminal velocity A tall glass jar or a tube fitted with a secure bung at its lower end about 5 em in diameter and 50 em in height is filled with glycerin and supported vertically (Fig. 13.16). Small bearing balls handled with tweezers are then allowed to fall centrally down the tube by dropping […]
Fluid friction Friction between solids was dealt with in chapter 2. We shall now say something about friction in fluids. Bodies moving through fluids, i.e., liquids or gases, experience a retarding force otherwise known as fluid friction or viscous drag. This is a factor involved in the design of ships, aircraft, and. other vehicles. In order to achieve […]
Industrial applications of metallurgical studies The behavior of metals and alloys under stress is important in connection with the forging of metal components. In this process the hot or cold metal is squeezed or hammered into shape instead of being cast in a mould (Fig. 13.11 and 13.12). Fig. 13.13 shows the crystal grain flow which takes place […]
Hooke’s law During the time London was being rebuilt after the great fire of 1666 a great deal of research went on in connection with building construction and the strength of materials. Robert Hooke, who was Chief Surveyor to the City of London, took a leading part in this work and extended his researches to include an investigation […]
Strength of materials. Elasticity Before various materials are used in the construction of machinery and buildings, tests are carried out to ensure that they are able safely to stand up to the stresses to which they are likely to be subjected. Industrial laboratories have special apparatus for carrying out these tests. Brittle substances such as masonry and cast iron […]
Osmosis Before cooking dried fruits such as prunes and apricots it is customary to lea soaking in cold water for some hours so that they swell up and become rest far as possible, to their original condition. During this time water passes through cell walls of the fruit by a process called osmosis. Osmosis can be demonstrated […]
Adhesion and cohesion The force of attraction between molecules of the same substance is called cohesion, distinct from adhesion or the force between molecules of different substances. The adhesion of water to glass is stronger than the cohesion of water. Hence, . ‘hen water is spilled on a clean glass surface it wets the glass and spreads out […]
Molecular explanation of surface tension On page 140 we explained that the molecules of a liquid are constantly oscillating to and fro alternately exerting repulsive and attractive forces on one another, yet free to move in the body of the liquid, exchanging partners as they go. Application of the kinetic theory, together with knowledge of how the force between […]
Further illustrations of surface tension We have already seen that soap solution, detergents, and alcohol will lower surface tension of water. Camphor has a similar effect. When a piece of champion thrown on to the surface of water it slowly dissolves and causes a reduction surface tension in its immediate neighbourhood. The stronger pull exerted by surrounding uncontaminated […]
Surface tension Most people are aware that an ordinary sewing needle can be made to float on water The experiment works best if the needle is slightly greasy. Usually, the needle is placed on a small piece of filter paper, which is then gently placed on the water surface. Within a few seconds the paper sinks to […]