(a) When we put our ear to a railway line, we can hear the sound of an approaching train even when the train is far off but its sound cannot be heard through the air. Why ?
(b) How could you convince a small child that when you speak, it is not necessary for air to travel from your mouth to the ear of a listener ?
(a) When we put our ear to a railway line, we can hear the sound of an approaching train even when the train is far off but its sound cannot be heard through the air. Why ?
(b) How could you convince a small child that when you speak, it is not necessary for air to travel from your mouth to the ear of a listener ?
a)
Because track of train is a solid material and due to its density the sound can travels more faster in railway (iron) track than in air, so the sound heard while putting our ear on the track will reach before.
b)
Sound is a form of mechanical wave which requires a medium to propagate. It travels in such a way that particles of the medium travel to and fro about their mean positions and during collisions with successive particles, energy gets transferred. The medium particles return to their original positions after the energy transfer (sound energy) takes places. Thus, the energy disturbance gets propagated further along.
In this way, the sound produced upon speaking travels from the mouth to ear without the actual displacement of the medium particles or the medium (air) itself.
a)
Because track of train is a solid material and due to its density the sound can travels more faster in railway (iron) track than in air, so the sound heard while putting our ear on the track will reach before.
b)
Sound is a form of mechanical wave which requires a medium to propagate. It travels in such a way that particles of the medium travel to and fro about their mean positions and during collisions with successive particles, energy gets transferred. The medium particles return to their original positions after the energy transfer (sound energy) takes places. Thus, the energy disturbance gets propagated further along.
In this way, the sound produced upon speaking travels from the mouth to ear without the actual displacement of the medium particles or the medium (air) itself.
