Physics

Sound

To Show That Solids and Liquids Cannot be Compressed but Gases Can be Compressed Easily

We take three 100 mL glass syringes having frictionless pistons. The nozzles of all the syringes are closed by inserting them in separate rubber corks so as to prevent leakage from them [see Figures 26(a), (b) and (c)]. Remove the pistons from all the syringes.
(1) In the first syringe, we fill common salt (which is a solid). Then insert the piston back into the syringe (after applying some vaseline to piston for its smooth movement) [see Figure 26(a)].
(ii) In the second syringe, we fill water (which is a liquid). Then insert the piston back into the syringe (after applying some vaseline to it) [see Figure 26(b)].
(iii) In the third syringe, we do not fill anything. It is already filled with air (which is a gas). We just put the piston back in it (after applying some vaseline to it) [see Figure 26(c)].

We now place 50 gram weight on the top of piston of each syringe to put pressure on common salt,water and air filled in them. We will observe that :
(a) The piston of first syringe containing common salt does not move down on putting weight [see Figure 26(a)]. This shows that on applying pressure, the volume of common salt in the syringe does not get reduced. This means that on applying pressure, the common salt does not get compressed (into a smaller volume). Since common salt is a solid, so in general we can say that a solid does not get compressed (on applying pressure).
(b) The piston of second syringe containing water also does not move down on putting weight [see Figure 26(b)). This also shows that on applying pressure, the volume of water in the syringe does not get reduced. This means that on applying pressure/the water does not get compressed (into a smaller volume).Since water is a liquid, so in general we can say that a liquid does not get compressed (on applying pressure).
(c) The piston of third syringe containing air moves down considerably on putting weight [see Figures 26(c) and (d)J. This shows that on applying pressure, the volume of air in the syringe is reduced. This means that on applying pressure, the air gets compressed (into a smaller volume). Since air is a gas, so in general we can say that a gas can be compressed easily (by applying pressure).
Gases have high compressibility. They can be compressed into very small volumes by applying large pressures. Due to its high compressibility, fairly large mass of a gas can be put in a small metal cylinder by compression. Such gas cylinders can be transported conveniently from one place to another. The cooking gas ( Liquefied Petroleum Gas, LPG) which we use in our homes is a compressed gas. 1The oxygen gas supplied to hospitals 'in cylinders is also in compressed 4 form. And compressed natural gas (CNG) filled in cylinders is being used increasingly as a fuel to run vehicles like cars and buses.

Notes

Sound - Notes

1. 3. Humidity of Air