Further developments In recent years, other applications of air lubrication have been explored such as the hovercraft which travels over water or land on a cushion of air. Fig. 2.7 shows the French Bertie trainer. Powered by an aircraft engine, it sat astride an inverted T – shaped rail and rode on a cushion of compressed air provided […]
Air lubrication As long ago as 1854, the French scientist, Gustav Him, suggested the use of air as a lubricant, but nearly a century was to pass before this idea was taken up seriously. Of recent years, research has been carried out at the National Engineering Laboratory at Killdeer in the development of air lubricated bearings and these […]
Lubrication While friction is highly essential in some circumstances, It IS a great nuisance in others. In a car engine, for example, oil under pressure is supplied continuously to all bearing surfaces. Failure of the oil supply will allow metal-to-metal contact and the resultant friction often raises the temperature and causes the bearing and pistons to “seize up”. Although […]
Friction and brakes The brake linings of automobiles and industrial machinery are commonly made from woven or molded material incorporating the mineral asbestos. This has good frictional properties and much research has been carried out in the manufacturer’s research laboratories to produce a strong, hard-wearing material with freedom from fade. Fade is the name given to the loss of […]
The nature of friction We shall now discuss briefly the nature of .frictional force. Primarily it depends on the composition of the surfaces, and we are here concerned with the friction between certain smooth surfaces rather than the obvious interlocking of projections which occurs with rough surfaces. Much research as been done on the subject of friction from […]
Coefficient of friction If the simple experiments we have described are repeated with various weights on the block it is found that both the static and the kinetic friction are increased roughly in simple proportion to the force, perpendicular to the surfaces, which is pressing them together. The ratios of the static and kinetic friction to the force […]
Kinetic or sliding friction If the block is pulled along so that it slips at a steady speed we notice that the spring balance gives a reading rather less than the static friction. Kinetic friction is, therefore, less than static.
Static friction A rectangular block of wood placed on a flat surface has a string and spring balance attached to it so that a horizontal force can be applied (Fig. 2.4). If a gradually increasing force is applied to the block it will, at first, continue to remain at rest since an equally increasing but oppositely directed […]
Friction Friction is the name given to the force which opposes the relative sliding motion of two surfaces in contact with one another lIt plays a notable part in our daily lives. For example, we are reminded of the importance of friction every time we slip up on an icy pavement or a polished floor. Walking would be […]
Artificial weight in a spacestation Weightlessness in a space vehicle is highly inconvenient to an astronaut in many ways. For example, he cannot pour liquid into a cup, neither can he drink from it: controlled movement is possible only by the use of handrails and so on. lt has been suggested that the space stations of the future […]