A surfer takes advantage of a wave’s energy to catch an exciting ride The ocean wave that this surfer is riding is just one type of wave Besides water waves, waves are also responsible for light, sound, and even earthquakes From music to television, waves play an important role in your life every day We will learn about the properties of waves and how waves interact with each other and everything around them. A wave is any disturbance that transmits energy through matter or space Examples of waves: – Water waves in the ocean – Microwaves inside the microwave oven – Light waves from the sun – Radio waves transmitted to the radio – Sound waves from the radio, telephone and voices Energy can be carried away from its source by a wave The material through which the wave travels does not move with the energy Sound waves often travel through air, but the air does not travel with the sound If air were to travel with sound, you would feel a rush of air every time you heard the phone ring. Some waves transfer energy by the vibration of particles in a medium A medium is a substance through which a wave can travel A medium can be a solid, a liquid, or a gas When a particle vibrates, it can pass its energy to a particle next to it As a result, the second particle will vibrate in a way similar to the first particle In this way, energy is transmitted through a medium Sound waves require a medium Sound energy travels by the vibration of particles in liquids, solids, and gases If there are no particles to vibrate, no sound is possible Other waves that require a medium include ocean waves, which travel through water, and seismic waves that travel through the ground Waves that require a medium are called mechanical waves Some waves can transfer energy without traveling through a medium Visible light is an example of a wave that doesn’t require a medium Other examples are microwaves produced by microwave ovens, TV and radio signals, and X rays used by dentists and doctors Waves that do not require a medium are called electromagnetic waves. Although electromagnetic waves do not require a medium, they can travel through substances such as air, water, and glass Light from the sun is a type of electromagnetic wave Light waves from some stars and galaxies travel distances so great that they can only be expressed in light years. A light year is the distance that light travels in a year. Some of the light waves from these stars have traveled billions of light years before reaching Earth. This means that the light that we see today from some distant stars left the star’s surface before the Earth was formed. Waves can be classified based on the direction in which the particles of the medium vibrate compared with the direction in which the waves travel. The two main types of waves are transverse waves and longitudinal waves. Waves in which the particles vibrate with an up-and-down motion are called transverse waves. The particles in a transverse wave move across, or perpendicular to , the direction that the wave is traveling. The highest point of a transverse wave is called a crest The lowest point between each crest is called a trough In a longitudinal wave, the particles of the medium vibrate back and forth along the path that the wave travels. A section of a longitudinal wave where the particles are crowded together is called a compression A section where the particles are less crowded than normal is called a rarefaction Compressions and rarefactions travel along a longitudinal wave much in the way the crests and troughs of a transverse wave move from one end to the other A sound wave is an example of a longitudinal wave Sound waves travel by compressions and rarefactions of air particles.