# What is a Torricelli vacuum

## Understanding Physics 2, Student Book

64 3  Workbook page 37 Measuring the air pressure 1. What did Evangelista Torricelli find out about the size of the air pressure? Water in the inverted glass (Fig. 64.1) E1 Fill a glass with a smooth rim with water. Put a postcard on top, hold it and turn the glass over. The card sticks to the glass. The water does not flow out. In experiment V1 you can see that the external air pressure is so strong that it can hold the water in the glass. But how high can the water column be that the air pressure can hold it? Water in the hose (Fig. 64.2) E1 Fill an approximately 11m long transparent hose with water and place it in a tub of water. Seal one end with a stopper. Pull the locked end up in the stairwell. The other end should stay in the tub. From a height of about 10m, the water column is no longer held by the air pressure. The excess water flows back into the tub, there is a vacuum in the hose above. The Italian physicist Evangelista Torricelli (1608–1647, Fig. 64.3) carried out a similar experiment. However, he used mercury instead of water. At normal air pressure, the mercury column remains about 760mm high in the closed part of a U-tube. From this he developed the mercury barometer (Figs. 64.4 and 64.5). Torricelli is also considered to be the discoverer of the vacuum, the vacuum. However, this was heavily questioned at the time. It was believed that a vacuum could only be found in Torricelli's head. 2. How strong is the air pressure at sea level? The air pressure can hold a column of mercury 76 cm high or a column of water about 10 m high. If the water column has a base area of ​​1 cm 2, this results in a mass of around 1 kg and a weight of around 10N. Therefore, the air presses with a force of about 10N per cm 2 = 1 bar or 1,000 hPa. V1 64.1 Water in the wrong glass V2 11m long PVC hose (transparent) Water 64.2 Water in the hose Info box: The air pressure (approx. 1 bar) can hold a water column of approx. 10m height. 64.3 Evangelista Torricelli invented the mercury barometer and created a vacuum for the first time. 64.4 Scale of an old mercury barometer vacuum mercury air pressure air pressure 760 mm weight pressure of the mercury column 64.5 Two types of mercury barometers: siphon and pear barometer Torricelli found out that the unidirectional air pressure at sea level keeps a 760 mm high mercury column in equilibrium can. M dynamometer adhesive hook glass plate 64.6 A strong suction cup For testing purposes only - property of the publisher öbv

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