Waves Basics What is a mechanical wave A

Waves Basics

What is a mechanical wave? Ø A mechanical wave is a disturbance in matter that carries energy from one place to another. Ø The matter which the wave travels through is the medium.

What causes a mechanical wave? Ø A mechanical wave is caused by a source of energy producing a vibration that travels through the medium.

Two types of Mechanical Waves Ø There are two types of waves: l l Transverse Longitudinal

Transverse Waves ØThe movement of the wave is at a right angle to the medium l Examples: • Light • Water waves • Electromagnetic waves

Parts of a Transverse Wave

Parts of a Transverse Wave Ø Midpoint: The point at which the medium was at rest before the wave. Ø Crest: The highest point of the wave above the midpoint. Ø Trough: The lowest point of the wave below the midpoint.

Longitudinal Waves ØThe direction of wave travel occurs along the direction in which the source vibrates. ØThis causes the medium to be temporarily compressed and stretched.

Parts of a Longitudinal Wave

Parts of Longitudinal Waves ØCompression – areas where the medium is closer together. ØRarefaction – areas where the medium is stretched apart.

Frequency Ø The number of vibrations in a given time (1 second) Ø Frequency = # of waves ÷ # of seconds l Unit of frequency is the Hertz • I cycle per second • 1 wave per second

Example Problem: Ø A pendulum completes one cycle every two seconds. What is the frequency of the pendulum?

Answer Ø Frequency = # of cycles ÷ # of seconds. l l Frequency = 1 cycle ÷ 2 seconds Frequency = 0. 5 Hertz

Wavelength Ø Wavelength is the distance between a point on one wave and the same point on the next cycle of the wave. Ø Frequency and wavelength are related. l l As the frequency increases, the wavelength decreases. As the frequency decreases, the wavelength increases.

Period Ø The amount of time it takes a wave to complete one cycle. Ø Period = 1/Frequency l Unit is seconds

Example Problem: Ø A pendulum completes 4 cycles in 3 seconds. l l What is the frequency of the pendulum? What is the period of the pendulum?

Answer: Ø Frequency = # cycles ÷ # of seconds l l Frequency = 4 cycles ÷ 3 seconds Frequency = 1. 3333 hertz Ø Period = 1/ Frequency l l Period = 1/1. 3333 Period = 0. 75

Wave Speed ØTwo possible formulas: Wave speed = wavelength x frequency OR l Wave speed = wavelength /period l

Example Problem: Ø In 30 seconds, 2 waves hit a dock. wavelength is 5 m. l l What is the frequency of the wave? What is the wave-speed? The

Answer: Ø Frequency = cycles ÷ time l l Frequency = 2 waves ÷ 30 seconds Frequency =1/15 hertz Ø Wave speed = Wavelength x frequency l l Wave speed = 5 m x 1/15 hertz Wave speed = 0. 33 m/s

Amplitude Ø Amplitude is the maximum displacement of the medium from its rest position.