English Practice for Engineers [antikvár]

1 Report Writing Section A PRESSURE AND BUOYANCY OF AIR Since air is an invisible gas, you may almost forget that it exists except when you meet its resistance in running or riding, or when you feel the force ofthe wind. As a matter of fact, air has weight and exerts pressure in much the same manner as water does. This pressure is sufficient to support a column of water approximately 34 feet high, or a column of mercury 76 centimetres high at sea level. Not only does air exert pressure, but it also tends to lift objects in much the same manner as water does. In other words, air has buoyancy, and Archimedes' principle applies to gases just as it applies to liquids. According to this principle, an object immersed in a gas is buoyed up by a force equal to the weight of the gas displaced. A familiar example of the buoyancy of air is found in the ascent of a balloon. REPORT OF AN EXPERIMENT TO FIND THE BUOYANCY OF AIR glass tube clamp Fig. 1 To find the buoyancy of air the following equipment was required: a round-bottomed flask of one-litre capacity; a rubber stopper for the flask; some glass tubing; some rubber tubing; a clamp; a measuring glass; an exhaust pump; ajar of 8-pint capacity; a balance; weights; and water. Method: The equipment was assembled as shown in Fig. 1. When it had been assembled, a rubber stopper was inserted in the glass flask. The equipment was weighed in grammes. This weight included the weight of air in the flask. The weight was Once it had been weighed, the flask was attached to an exhaust pump by the open end of the rubber tube, and part of the air was drawn away from the flask. Care was taken to make sure that the flask did not break as a result of the greater pressure outside. The clamp on the rubber tube was closed, and while it was closed, the flask with its attachments was weighed. The weight of the equipment including ¦i i f