![]() In solids, however, they travel both as longitudinal and transverse waves. Sound waves propagate as longitudinal waves in fluid media. So the air/water molecules are displaced in the same direction as the direction of propagation. The air particles vibrate parallel to the direction. Thus we see that the transverse wave of in the x-direction leads to a disturbance velocity involving only the x-component velocity u. Sound wave is called longitudinal wave because it is produced by compressions and rarefactions in the air. The solution to the above equation is given as,įrom this solution and the definition of the velocity potential ( ), we can find the disturbance velocity field as, (This equation is derived from the Navier-Stokes equation after linearization and some other assumptions). During sound propagation in the x-direction, the velocity potential obeys the wave equation. When sound propagates from left to right, the air molecules are compressed and rarefied just like the vertical grid lines in the above figure. This is illustrated in the following image: (taken from Wikipedia) On the other hand, we have longitudinal waves where the displacement of the medium occurs in the same direction as that of wave propagation. An illustration of a transverse wave is given below: (taken from Wikipedia) This kind of wave is called a transverse wave. Thus we say, the wave propagates in one direction and the displacement of the medium is at right angles to that direction. In a longitudinal wave the particles move parallel to the direction the wave is moving. But the change itself makes the water go either up/down at a given location. A slinky can easily demonstrate the two basic types of waves, longitudinal and transverse. In the example given above, the change in the water level is propagating outwards throughout the pond. And this change is propagated through space. This means that the vibration of the wave travels in the same direction as the wave itself. These pressure waves are what we hear as sound. These vibrations cause the air molecules to move back and forth, creating pressure waves. Similarly, for a light wave, the thing that changes is the electromagnetic field. Sound waves are created by vibrations that travel through the air, or any other medium. In this case, is the displacement of water from the undisturbed level. This change propagates through the pond from the source that created the disturbance. Everything that makes a sound must have a part that vibrates. For example, in the case of a ripple in a pond, a change in the height of the water plays the role of the disturbance. The solution to the above equation is any (good!) function traveling in the x-direction with speed c. Most wave phenomenon we see in nature are governed by the so-called wave equation, In simple terms, a wave is a disturbance propagating through a medium (say, air or water). Hence, even though propagates like a transverse wave, the disturbance velocity propagates like a longitudinal wave. ![]() This is related to the disturbance velocity in the following way,Īnd from vector analysis, it is easy to show that the gradient vector is perpendicular to constant lines of the original field. In the case of a sound wave, the variable governed by the wave equation is the velocity potential. But in case of a light wave or traveling waves on a string, the variable governed by the wave equation is the disturbance itself. Short Answer:īoth light propagation and sound propagation (in air or water) are governed by the same wave equation. This is how sound waves travel along through solids, liquids and gases. These vibrations are passed along to nearby particles, which then pass them on again. ![]() ![]() Sound waves can travel through a vacuum because they dont require particles. But we do not often ask the question ‘Why?’. The vibrations in a longitudinal wave are to the direction of energy transfer. Moreover, we are told that sound waves are longitudinal waves (compression waves) and light waves are transverse waves. Thats the usual answer we think about when asked that question. \) is a reference sound intensity at about the threashold of human hearing.“Give me some example for waves in nature! ” ![]()
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