HomeSCIENCE FACTSPHYSICS FACTSHow does sound travel? Sound is transmitted by particles (atoms or molecules) in a solid, liquid or gas colliding with each other. It is a wave which is created by vibrating objects and propagated through a medium (solid, liquid or gas) from one location to another. A vibrating source can be sound coming from a drum, speaker of a radio, the mouth of a person (vocal chord), a car engine, a plane above the sky and so on. Although sound is commonly associated in air, sound will readily travel through many materials that are solid, liquid and gas. 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 particles are constantly moving and so the particles change their position, but they are not fixed to each other that strongly as they are in a solid. They can also vibrate and collide with other of their particles over a short range; sending sound waves through it. This is because the attractive forces among the particles 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 slightly less fast through liquids. In gas, particles in gases are very far apart from each other. They can vibrate as well as move freely and randomly in all direction. This is due to the fact that the force of attraction between the particles 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 particles 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. While sound will readily travel through many materials, in order for us to hear it, it will have to travel through the air to reach our ears (eardrum). Your eardrum vibrates from sound waves to allow you to sense them. We might be able to detect it through vibration of solids, the ripple in liquid but you can only detect it in air by hearing it. In spite of this, humans cannot hear all sounds that travel through the air. It will have to be at a certain decibel for us to hear it. For e.g. dogs can hear sounds that are not able to be detected by humans. Sound can also be detected by other means other than hearing it. Sounds traveling in any of the three states can be detected using electronic detectors. E.g Microphones Sound (in air) is made when air molecules vibrate and move (away from the vibrating source) in a pattern called waves, or sound waves. Sound is a mechanical, longitudinal wave (that moves in all directions) and travels in waves of compressions and rarefactions (expansion) as it successively passes through a medium. CLICK THE FIRST IMAGE BELOW TO SEE HOW THE PARTICLES MOVE Air particles moves in a to and fro position where they collide with each other to form a cluster (compression) then they rebound from each other, the same effect of hitting a ball against a wall (rarefaction) – i.e. a series of mechanical compressions and rarefactions. Sounds are carried this way by the air particle in a outward fashion similar to ripple in a pond as it continues to collide with air particles. The air particles do not move over a large area but, carry the sound by colliding with other air particles. This way it passes on the vibration similar to a domino effect, as it moves away from the vibrating source. Vibrations of frequencies in the approximate range of 15 to 20,000 hertz, can be detected by human ears.