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SC.7.P.10.3 Recognize that light waves, sound waves, and other waves move at different speeds in different materials. Bell Ringer • Because sound is energy created by vibrations, through which medium will it move the fastest? • Gas • Liquid • Solid • Vacuum • Radars can help meteorologists detect clouds and sailors detect submarines. Radars send out radio waves and record their echoes after the radio waves reflect off an object. Two radars send out radio waves with the same frequency. The first radar sends radio waves through the air. The second radar sends radio waves through the ocean. What is true about these radio waves? • They are visible C. They have different speeds. • They are audible D. They have the same wavelength.
The light slowed down. All waves travel at different speed in different media. Air and water are examples of media. What do you think a medium is? (Media is the plural of medium)
Sound also changes speed in different media Sound travels much faster in water than in air. This allows dolphins to communicate quickly across large distances.
Left Side Right Side • The speed of a wave through a substance is determined by the substance’s physical properties. Light, like all electromagnetic waves, consists of vibrating electric and magnetic fields. The speed of light through a substance depends on the substance it interacts with. • Light waves move fastest in gases. Light does not interact with matter. So, the less matter in a medium, the faster the light can travel. • The speed of sound waves is also affected by the substance it interacts with. • Sound and other mechanical waves move fastest in solids. Since sound waves travel by moving mater, the more densely packed the medium, the faster light can travel. • When waves move from one medium to another medium, the waves slow down (or speed up) resulting in a change of direction. This change in direction is called refraction. • Sometimes, a wave cannot travel through a medium. Instead, a wave can either be reflected off a surface (an echo, for example), or absorbed by the medium, like tints on a window.
Exit Slip The picture above shows a bird landing at a bird feeder outside a window. The image of this bird in the window is the result of light being (A) absorbed (C) transmitted (B) reflected (D) refracted 2. Two people witness lightning striking a tree during a severe thunderstorm. Both people are the same distance from the lightning, but one person sees the lightning first. Which statement best describes a situation where this is possible? • One individual is north of the lightning strike in an open field, while the second person is to the west of the lightning strike in a crowded neighborhood. • One individual is on the roof of a building, while the second person is outside the front door of the building. • One person is on a boat in the ocean, while the second person is scuba diving under the boat. • One person is standing in the rain, while the other person is not in the rain. Sound waves are a type of mechanical wave. Using the characteristics of various media, explain through which type of medium do sound waves travel fastest?