A Wave
Waves are vibrations that transfer energy from place to place without matter (solid, liquid or gas) being transferred.

Some waves must travel through a substance. The substance is known as the medium and it can be solid, liquid or gas. Sound waves and seismic waves are like this. They must travel through a medium, and it is the medium that vibrates as the waves travel through.
This waves are called Mechanical waves.

Other waves do not need to travel through a substance. They may be able to travel through a medium, but they do not have to. Visible light, infrared rays, microwaves and other types of electromagnetic radiation are like this. They can travel through empty space. Electrical and magnetic fields vibrate as the waves travel.

This waves are called Electromagnetic waves.


Types of waves:
Waves can be longitudinal or transverse.

1- The longitudinal waves:
In longitudinal waves, the oscillations are along the same direction as the direction of travel and energy transfer.
Sound waves and waves in a stretched spring are longitudinal waves. 

Longitudinal waves show areas of compression and rarefaction.

 In this animation , the areas of compression are where the parts of the spring 

are close together,while the areas of rarefaction are where they are far apart.


What happen to the particles of a medium while a longitudinal wave is travelling through it?

The particles of the medium are displaced in a direction parallel to energy transport. As one individual particle is disturbed, it transmits the disturbance to the next interconnected particle. This disturbance continues to be passed on to the next particle. The result is that energy is transported from one end of the medium to the other end of the medium without the actual transport of matter. In this type of wave - a longitudinal wave - the particles of the medium vibrate in a direction parallel to the direction of energy transport.

2- Transverse waves: 

Have a look at this example: a group of people jump up and sit back down, in sequence

note that something (we could call it information) travels from left to right, 

but the people themselves only stand up and sit down - no-one swaps seats.

 Here the medium in which the wave propagates is 'people'...no people=no waves.

 This is a transverse wave which is transmitted by vibrating particles (in this case the 

particles are the people), but although they oscillate (stand up / sit down) the particles do not 

move from their normal position.

A big transverse wave in a stadium

 The movement of the people is vertical (up and down) whereas the wave travels horizontally (from left to right). In the transverse 

wave - the vibration direction is perpendicular (at right angles) to the direction in which the wave travels or propagates. Transverse 

waves are very common - waves in water and on strings are two good examples..

The difference between the longitudinal and  transverse wave can  be clear by using a slink spring y spring

A transverse wave is a wave in which particles of the medium move in a direction perpendicular to the direction that the wave 
moves. Suppose that a slinky is stretched out in a horizontal direction across the classroom and that a pulse is introduced into the slinky on the left end by vibrating the first coil up and down. Energy will begin to be transported through the slinky from left to right. As the energy is transported from left to right, the individual coils of the medium will be displaced upwards and downwards.
Examples on the transverse wave: ripples on water, light and all the electromagnetic waves.

What happen to the particles of a medium while a transverse wave is travelling through it?
 In this case, the particles of the medium move perpendicular to the direction that the pulse moves.
Transverse waves are always characterized by particle motion being perpendicular to wave motion.

Press on the link below to check the motion of the particles by using this model 

                                                                                 Wave on a string 

There are some parameters that describe the wave:
1- wavelength.
2- Amplitude.
3- Frequency .
4- wave speed.  

Other topics that will be covered in this unit:
  1. light refraction.
  2. Dispersion of light (Converging lens) .
  3. Ultra sound.