To control noise effectively, it's important to distinguish between the two types of sound and the medium in which it propagates. Sound waves are a form of elastic waves that occur in any medium that has mass and elasticity. When mass (inertia) enables disturbed particles to transfer energy to the adjacent particle, elasticity enables the disturbed particle to get back to its original position, like a spring. This propagation of momentum from one particle to another explains the manner in which sound waves travel.