PHYS 20 LESSONS Unit 6: Simple Harmonic Motion Mechanical Waves Lesson 6: Mechanical Waves

Reading Segment: Mechanical Waves To prepare for this section, please read: Unit 6: pp

MECHANICAL WAVES There are two types of mechanical waves: 1. Transverse Waves - wave motion is perpendicular to particle vibration 2. Longitudinal Waves - wave motion is parallel to particle vibration

Transverse Waves Consider a vertical vibration at the end of a spring: spring (medium) Vibration

wave motion Vibration The vibration is the source of energy for the wave. It creates a disturbance in the medium, moving away from the source.

wave motion Vibration All particles are vibrating perpendicular to the wave motion. They never move left or right. Thus, it is called a transverse wave.

Crests Vibration Troughs The top of the transverse wave is called the crest. The bottom of the wave is called the trough.

Equilibrium Vibration The rest position of the medium is called the equilibrium position. This is where the particles would be if there was no wave going through it.

A Vibration The maximum amplitude (A) is the energy of a wave. It is the distance from equilibrium to the crest (or from equilibrium to the trough).

Vibration The wavelength ( ) is the length of 1 cycle or repetition of the wave.

Vibration The wavelength could be the length from crest to crest.

Vibration The wavelength could also be the length from trough to trough.

Vibration Note: If two particles are one wavelength apart, they will move identically as the wave train goes through the medium. We say that they are in phase.

Animations Transverse Waves Go to: "Waves" "Transverse Waves"

Animations Anatomy of Transverse Waves 1. aveParts.htm aveParts.htm 2. ductionWaves.html ductionWaves.html

Longitudinal Waves Consider a horizontal vibration at the end of a spring: Vibration spring (medium)

Direction of wave Vibration The vibration is the source of energy, and it causes a horizontal disturbance in the medium. The wave moves away from the source.

Direction of wave Vibration The particles are always vibrating parallel to the wave motion. Thus, this is called a longitudinal wave.

C C C C Vibration R RR R The regions of high density are called compression (C) regions. The regions of low density are called rarefaction (R) regions.

Vibration C C The wavelength of a longitudinal wave is the distance between two successive compression regions i.e. "from C to C"

Animations Longitudinal Waves Go to: "Waves" "Longitudinal Waves" "Transverse Waves"

Note:  Due to friction, waves will lose their energy - transverse waves lose their amplitude - longitudinal waves will lose their density But, the frequency will never change.

 Surface waves (e.g. water waves) are circular waves

Upper particles move in circles Lower particles move in ellipses Deep particles move back and forth

 Earthquakes create all 3 kinds of waves Primary (P) waves - the first to arrive - longitudinal waves Secondary (S) waves - second to arrive - transverse waves Surface waves - last to arrive - these do the most damage

Animation Earthquakes 1. main.html main.html