We use many simple devices in our everyday life which work on the existence of atmospheric pressure. For example, the devices such as a drinking straw, a syringe, a dropper and a rubber sucker work on the existence of atmospheric pressure (or air pressure) around us. We will now describe all these devices, one by one. Let us start with a drinking straw.
1. DRINKING STRAW. The drinking straw is a very thin pipe which is used to drink to drink soft drinks (like Coca-Cola and Pepsi). The working principle of the straw is the presence of atmospheric pressure. This can be explained as follows : The lower end of drinking straw is dipped in the soft drink. When we suck at the upper end of the straw with our mouth, the pressure of air inside the straw and in our mouth is reduced. But the pressure acting on the surface of the soft drink is equal to atmospheric pressure. So, the greater atmospheric pressure acting on the surface of the soft drink pushes the soft drink up the straw into our mouth.
2. SYRINGE. A glass tube (or plastic tube) with a nozzle and piston for sucking in and ejecting liquid in a thin stream is called a syringe (A syringe may also be fitted with a hollow needle for giving injections). The principle of operation of the syringe is the presence of atmospheric pressure. When the nozzle of a syringe is dipped in a liquid and its piston is withdrawn, the pressure inside the syringe is lowered. The greater atmospheric pressure acting on the surface of the liquid pushes the liquid into the syringe.
3. DROPPER. The dropper is a short glass tube with a rubber tube at one end and a nozzle at the other end. A dropper is used for measuring out drops of a liquid (such as a liquid medicine). A dropper works on the existence of atmospheric pressure. When we press the rubber bulb of the dropper by keeping its nozzle dipped in the liquid, air present in the glass tube and bulb is seen to escape in the form of bubbles. Due to this, the air pressure inside the glass tube and rubber bulb of dropper is very much reduced. When we now release the rubber bulb of dropper, the much greater atmospheric pressure acting on the surface of liquid, pushes the liquid u into the drdopper tube. Thus, the rise of liquid (say, water) in a dropper is due to the atmospheric pressure. If we remove the filled dropper from the container of liquid and press its rubber bulb slowly, then the drops of liquid will come out of the nozzle of dropper tube. Just like a dropper, the filling of ink in a fountain pen is also based on the existence of atmospheric pressure.
4. RUBBER SUCKER. A sucker is a device made of rubber (or plastic) that sticks firmly to flat and smooth surfaces on pressing. The rubber suction cup looks like a small concave rubber cup. A rubber sucker is also called a ‘suction cup’ because it sticks to a surface by suction (The production of partial vacuum by the removal of air is called suction). When we press the rubber suction cup onto a flat, smooth surface, the concave rubber cup will flatten to a large extent, pushing most of the air out of it. Since very little air remains inside the flattened rubber sucker, therefore, from beneath it. There is very little air remaining inside the flat rubber suction cup.