Features of a wave
Waves are vibrations of energy that transfer from place to place. Waves have no mass so no matter is transferred if waves are. Most waves travel through the air and in vacuums at light speed but some waves must travel through substances. The substance is known as the medium which can be solid, liquid or gas. Sounds waves must travel through a medium and it is the medium that vibrates as the sound travels through allowing many people to hear sounds at the same time.
Other waves do not need to travel through a medium. They can travel through a medium but it is not necessary for movement. All the waves of the electromagnetic spectrum are like this. The thing that allows these waves to move is the electrical and magnetic fields vibrating with the wave.
When waves go through a gap in a barrier, they carry on through the gap however the wave extends after the gap and spreads out further than when it approached the gap. This is diffraction.
The extent of diffraction depends on how the width of the gap compares to the wavelength of the wave. The highest diffraction only happens when the wavelength is of the order of magnitude as the gap.
The amplitude of a wave is its maximum position from the middle rest position. The wavelength of a wave is the distance between a point on one wave and the same point on the next wave. It is easiest to measure the wavelength from the trough to the crest. Frequency is the number of waves produced by a source each second and the frequency is also the number of waves passing through a certain point each second. We measure frequency is hertz (Hz), however, most waves frequencies are measured in Kilohertz (kHz), megahertz (MHz) and gigahertz(GHz).
Waves can be longitudinal and transverse waves.
A transverse wave oscillates at right angles to the direction of travel and energy transfer. Examples of transverse waves include light and the waves on the electromagnetic spectrum with the wave shape being as in the diagram above.
A longitudinal wave oscillates in the same direction as the direction of travel and energy transfer. Sounds waves and waves in a spring are longitudinal waves.