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 MotionA 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:

1. reflection,

2. refraction,

3. diffraction, or

4. absorption.

23.3 Wave interactionsA 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 wavesThe oscillations of a longitudinal wave are in the same direction that the wave moves.

23.3 Constructive interferenceConstructive 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 interferenceWhat 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

Key Question:How do waves move?

Waves in Motion

Cell Phones: How they workThe 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.