There was a time, during the Renaissance, when scientists spoke of the "six simple machines". Building on ancient Greek and Roman understanding they identified these as the lever, the wheel and axle, the inclined plane, the pulley, the screw, and the wedge. Each of these uses a single force applied as work on a single load to produce mechanical advantage. All more complex (or "compound") machines, such as the wheelbarrow, windmill, trebuchet or shears, were seen as composed of multiples of the simple machines. The industrial revolution made this elegant, if somewhat basic, understanding insufficient as a way of describing machinery and forces. However, it retains a place in the teaching of physics.
These thoughts came to mind as I stood in a railway signal box at Bressingham the other day. I think it was the first time I'd been in such a building. This particular example had been moved from Raydon Wood, Suffolk, to be used with the railway exhibits at the Norfolk gardens. I was particularly taken with the levers in the lever frame that the signal man used to control points, signals, gates etc thereby facilitating the safe movement of a train through the area for which he had responsibility. I'd often seen these through the window of a signal box. However, the elevated position prevented me noticing what I could see now - they are colour coded, numbered and each has its purpose described. By manipulating single levers, or combinations of them, the signalman determined the course of the train. Today this is done electro-mechanically but for decades muscle power, augmented by the lever did all that was required.
photograph and text © Tony Boughen
Camera: Canon 5D2
Mode: Aperture Priority
Focal Length: 90mm
F No: f8
Shutter Speed: 1/80
ISO: 400
Exposure Compensation: -0.67 EV
Image Stabilisation: On
