# Pressure in liquids and gases

## A liquid finds its own level

A liquid finds its own level When water or any other liquid is poured into the communicating tubes shown in Fig. 10.9 it stands at the same level in each tube. This illustrates the popular saying that, “water finds its own level”. When the liquid is at rest in the vessel the pressure must be the same …

## To verify that pressure is proportional to density

To verify that pressure is proportional to density Starting with a large spring reading each time, various liquids of known density, fare poured in to the same depth. The balance is lowered and its reading noted whet the liquid just begins to escape. Alternatively, a straight line through the origin should be obtained if F is plotted against …

## To study the variation of pressure with depth in a liquid

To study the variation of pressure with depth in a liquid A glass tube, 2 or 3 em in diameter, with its lower end ground perfectly flat is clamped vertically over a large beaker. A flat metal plate attached by thread to a spring balance is held against the lower end of the tube (Fig. 10.8). The …

## Calculation of pressure in a liquid

Calculation of pressure in a liquid Suppose we consider a horizontal area A, in m-, at a depth of h, in m, below the surface of a liquid of density p, in kg/m3 (see Fig. 10.7). Standing on this area is II vertical column of liquid of volume hA, in m’, the mass of which (volume x …

## Pressure in a liquid

Pressure in a liquid Liquids exert pressure in the same way that air does. The pressure in a liquid increases with depth. This may be shown by means of a tall vessel full of water with side tubes fitted at different heights (Fig. 10.5).The speed with which water spurts out is greatest for the owest jet, showing that pressure …

## The vacuum pump

The vacuum pump The invention of the air pump by Otto von Guericke led to big advances in the study of air pressure. Fig. 10.4 shows the principle of a modern type of pump. Each time the piston is at the bottom of the cylinder some air from the vessel to be evacuated expands into the space above …

## The Magdeburg hemispheres

The Magdeburg hemispheres In 1654 a German scientist named Otto von Guericke made two hollow bronze hemispheres, one of which had a stop-cock. After the rims of these had been placed together with a greased leather ring in between to form an airtight joint the air was pumped out and the stop-cock closed (Fig. 10.3). Before this was …

## Crushing can experiment

Crushing can experiment The large forces which can be produced by atmospheric pressure may be demonstrated by means of a metal can fitted with an airtight stopper. The stopper having been removed, a small quantity of water is boiled in the can for a few minutes un the steam has driven out the air. The cork is then …

## Atmospheric pressure

Atmospheric pressure. Here on earth we are living at the bottom of a sea of air. Air has weight, and later in this chapter we shall show how its density can be measured. Owing to its weight the atmosphere exerts a pressure at the surface of the earth of approximately 100000 N/m2 (or 100 kPa). Now the atmospheric …

## Pressure in liquids and gases

Pressure in liquids and gases “Pressure” is a word we use from day to day without worrying too much as to its exact meaning. Before setting out on a car journey we make sure that the air pressure in the tyres has been correctly adjusted, not only to keep within the law, but for our own safety and …