The vibrations are then transferred though the environment from neighbour to neighbour. This energy transfer is called wave motion. Waves move energy through a medium without moving the whole medium. Types of waves Longitudinal waves When waves transfer energy by pushing neighbours in the same direction that the energy moves, the waves are called longitudinal waves. The places when the particles cluster together are volumes of high pressure so these waves are also called pressure waves.
Sound waves are an example of pressure waves and they can move through gases, liquids and solids.
For sound waves, the denser the medium the faster the speed. When waves transfer energy by pulling neighbours sideways to the direction of travel, the waves are called transverse waves. They all move at the same speed of 300,000 km.s -1 when they travel through vacuum. They slow down when they travel through a medium. Mechanically twisting or pulling a medium sideways is called shearing so waves formed this way are also called shear waves.