If you place your fingers on your throat while talking or humming, you can feel vibrations. If you see a stringed musical instrument like the Veena or the Sitar being played you can see its strings vibrating. If you strike its string gently to produce a sound and then touch it, you can feel the quivering metal wire. In fact all sounds are the results of vibrations. A body can produce sound when a part or the whole of it vibrates within certain frequencies. Our ears can hear only those sounds which are produced by vibrations of frequencies ranging between 20 and 20,000 vibrations per second.
Sound travels from one place to another in the form of waves which we cannot ‘see’ but can feel and hear. These waves need some medium to travel along. They cannot travel in vacuum. We live in an ocean of air, with our feet on the ground. This air is a good medium for sound to travel from place to place. Solids and liquids can also carry sound waves. A solid must be elastic for this purpose. The well known “string telephone” which all children like to make and play with, shows how a tightly stretched string can carry sound.
When sound travels through the air, the vibrating body pushes the air particles close to it and they pass on the disturbance to those next to them. The process goes on until the vibrations reach the ear drum which also vibrates and sends message to the brain. The temperature of air has a considerable effect on the speed of sound.
Sound is transmitted by tiny particles called as atoms or molecules in a solid, liquid or gas colliding with each other. Sound is a wave which is created by vibrating objects and propagated through a medium (solid, liquid or gas) from one distance to another or from one location to another. A vibrating source can be a sound coming from a flute, drum or stereo tape, a radio, the mouth of a person (vocal chord), a car engine, a plane above the sky and so on. There are many examples. Although sound is commonly associated in air, sound travel through numerous materials through solid, liquid and gas.
That being explained above, let us learn how sound travel through mediums of Solid, Liquid and Gas.
What are Solids? Solids are tangible and are hard in nature. Solids are made up of particles (atoms) that do not move about because they are closely packed touching each other and held together by strong intermolecular forces. Therefore, they are always in a fixed position and can only vibrate in a fixed position, sending sound waves along its path very fast. This is similar to a domino effect. This means that sound waves (produce from a vibrating source) is immediately transmitted by the vibrating particle in a fixed position by hitting the neighboring atom sending on the sound wave from one atom to the other throughout the solid object.
In liquid, the molecules are constantly moving and so the molecules change their position, but like solid they are not fixed strongly to each other. They can also vibrate and collide with other of their near molecules over a short distance; sending sound waves through it. This is because the attractive forces among the molecules of a liquid are sufficiently strong enough to hold them together but are not strong enough to hold them in a fixed position. As such, sound will travel in lesser speed through liquids compared to solid.
Molecules in gases are apart from each other. They vibrate, move freely and randomly in all direction. Because of this fact, that the force of attraction between the molecules are negligible. This means therefore, that there is no force of attraction between gas particles. Gas molecules must move quite a distance before they collide with other molecules. Sound energy cannot move as quickly when the molecules are not in contact with each other. Thus, since gas molecules are very far apart , sound waves traveling through this medium, will be much slower than that of a liquid and a solid respectively. Because of gas particles being everywhere on Earth, we can hear sound from all directions.