WAVES 23.3

Chapter Twenty-Three: Waves 23.1 Harmonic Motion 23.2 Properties of Waves 23.3 Wave Motion

Chapter 23.3 Learning Goals Distinguish between transverse and longitudinal waves. Demonstrate an understanding of wave interactions. Distinguish between constructive and destructive interference.

23.3 Wave Motion A wave front is the leading edge of a moving wave which is considered to be the crest for purposes of modeling. The crests of a plane wave look like parallel lines. The crests of a circular wave are circles.

23.3 Four wave interactions When a wave encounters a surface, four interactions can occur: reflection, refraction, diffraction, or absorption.

23.3 Wave interactions A boundary is an edge or surface where things change. Reflection, refraction, and diffraction usually occur at boundaries.

23.3 Wave interactions Diffraction usually changes the direction and shape of the wave. When a plane wave passes through a small hole diffraction turns it into a circular wave.

23.3 Transverse and longitudinal waves A wave pulse is a short ‘burst’ of a traveling wave. It is sometimes easier to see the motion of wave pulses than it is to see long waves with many oscillations.

23.3 Transverse waves The oscillations of a transverse wave are not in the direction the wave moves.

23.3 Longitudinal waves The oscillations of a longitudinal wave are in the same direction that the wave moves.

23.3 Constructive interference Constructive interference happens when waves add up to make a larger amplitude. Suppose you make two wave pulses on a stretched string. One comes from the left and the other comes from the right. When the waves meet, they combine to make a single large pulse.

23.3 Destructive interference What happens when one pulse is on top of the string and the other is on the bottom? When the pulses meet in the middle, they cancel each other out. During destructive interference, waves add up to make a wave with smaller or zero amplitude.

Investigation 23C Waves in Motion Key Question: How do waves move?

Cell Phones: How they work The process that allows a cell phone to communicate is the same as for a radio or walkie-talkie. All of these devices use electromagnetic waves of within a specific frequency range to send information.