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.
Earth is the medium for earthquake waves. Waves that can travel only through a medium are called mechanical waves. Most waves, including water waves, sound waves, and earthquake waves, are mechanical waves. Electromagnetic waves are the most common kind of nonmechanical waves. READING TOOLBOX Compare After you read this section, make a chart comparing transverse and longitudinal waves.