NOTE: Above figures include non-CSI data. last updated: Sept. 23, 2015 data sources. California Solar Statistics (CSS) is the official public reporting site of the California Solar Initiative (CSI), presented jointly by the CSI Program Administrators and the California Public Utilities Commission.
Sound can travel through air, water, or solids, but it can't travel through a vacuum. It needs the medium to help it travel. Other examples include water waves, seismic waves, and waves traveling through a spring. Electromagnetic waves are waves that can travel through a vacuum (empty space). They don't need a medium or matter. They travel through electrical and magnetic fields that are generated by charged particles. Examples of electromagnetic waves include light, microwaves, radio waves, and X-rays.
A wave on a string is the classic example of a transverse wave. Each part of the string moves up and down while the wave moves from side to side. Transverse waves can not happen in gases because the perpendicular motion is not created by any force. A Slinky is a great way to visualize longitudinal waves. Each part of the Slinky moves from side to side, just like the wave itself. Sound waves are longitudinal pressure waves in the air. Water waves involve a combination of transverse and longitudinal waves. The water moves up and down, but also back and forth.