How do particles move in a longitudinal wave

Longitudinal waves show areas of compression and rarefaction :. In the diagram, the compressions move from left to right and energy is transferred from left to right. However, none of the particles are transported along a longitudinal wave. In a longitudinal wave the particle displacement is parallel to the direction of wave propagation.

The animation at right shows a one-dimensional longitudinal plane wave propagating down a tube. The particles do not move down the tube with the wave; they simply oscillate back and forth about their individual equilibrium positions. Pick a single particle and watch its motion. The wave is seen as the motion of the compressed region ie, it is a pressure wave , which moves from left to right. The second animation at right shows the difference between the oscillatory motion of individual particles and the propagation of the wave through the medium.

The animation also identifies the regions of compression and rarefaction. The P waves Primary waves in an earthquake are examples of Longitudinal waves.

The P waves travel with the fastest velocity and are the first to arrive. This process continues along the chain of particles until the sound wave reaches the ear of the listener.

A detailed discussion of sound is presented in another unit of The Physics Classroom Tutorial. Waves traveling through a solid medium can be either transverse waves or longitudinal waves.

Yet waves traveling through the bulk of a fluid such as a liquid or a gas are always longitudinal waves. Transverse waves require a relatively rigid medium in order to transmit their energy.

As one particle begins to move it must be able to exert a pull on its nearest neighbor. If the medium is not rigid as is the case with fluids, the particles will slide past each other. This sliding action that is characteristic of liquids and gases prevents one particle from displacing its neighbor in a direction perpendicular to the energy transport. It is for this reason that only longitudinal waves are observed moving through the bulk of liquids such as our oceans.

Earthquakes are capable of producing both transverse and longitudinal waves that travel through the solid structures of the Earth. When seismologists began to study earthquake waves they noticed that only longitudinal waves were capable of traveling through the core of the Earth.

For this reason, geologists believe that the Earth's core consists of a liquid - most likely molten iron. While waves that travel within the depths of the ocean are longitudinal waves, the waves that travel along the surface of the oceans are referred to as surface waves.

A surface wave is a wave in which particles of the medium undergo a circular motion. Surface waves are neither longitudinal nor transverse. In longitudinal and transverse waves, all the particles in the entire bulk of the medium move in a parallel and a perpendicular direction respectively relative to the direction of energy transport. In a surface wave, it is only the particles at the surface of the medium that undergo the circular motion. The motion of particles tends to decrease as one proceeds further from the surface.

Any wave moving through a medium has a source. Somewhere along the medium, there was an initial displacement of one of the particles. For a slinky wave, it is usually the first coil that becomes displaced by the hand of a person. For a sound wave, it is usually the vibration of the vocal chords or a guitar string that sets the first particle of air in vibrational motion.

At the location where the wave is introduced into the medium, the particles that are displaced from their equilibrium position always moves in the same direction as the source of the vibration. So if you wish to create a transverse wave in a slinky, then the first coil of the slinky must be displaced in a direction perpendicular to the entire slinky. Similarly, if you wish to create a longitudinal wave in a slinky, then the first coil of the slinky must be displaced in a direction parallel to the entire slinky.

Electromagnetic versus Mechanical Waves. Another way to categorize waves is on the basis of their ability or inability to transmit energy through a vacuum i. Categorizing waves on this basis leads to two notable categories: electromagnetic waves and mechanical waves. As the vibrating string moves in the forward direction, it begins to push upon surrounding air molecules, moving them to the right towards their nearest neighbor. This causes the air molecules to the right of the string to be compressed into a small region of space.

As the vibrating string moves in the reverse direction leftward , it lowers the pressure of the air immediately to its right, thus causing air molecules to move back leftward. The lower pressure to the right of the string causes air molecules in that region immediately to the right of the string to expand into a large region of space.

The back and forth vibration of the string causes individual air molecules or a layer of air molecules in the region immediately to the right of the string to continually vibrate back and forth horizontally. The molecules move rightward as the string moves rightward and then leftward as the string moves leftward. These back and forth vibrations are imparted to adjacent neighbors by particle-to-particle interaction.