What are waves?

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What are waves? Water waves are just one of many kinds of waves. Sound and light are also waves. Waves are caused by vibrations of a medium. A medium is the material through which a wave can travel. Waves transfer energy from one place to another. Copyright © Houghton Mifflin Harcourt Publishing Company 3

There are two main types of waves Waves are classified by what they are travel through... SO…… There are two main types of waves Mechanical waves Electromagnetic waves

What are some types of waves? Waves such as water waves that require a medium are called mechanical waves. Copyright © Houghton Mifflin Harcourt Publishing Company 5

Mechanical Waves Some mechanical waves can travel through more than one medium. For example, sound waves can move through air, water, and a solid wall. Mechanical waves can’t travel without a medium. Copyright © Houghton Mifflin Harcourt Publishing Company 6

Electromagnetic Waves Electromagnetic (EM) waves are not disturbances in a physical medium. They are vibrations of electric and magnetic fields. Sunlight is an example of EM waves. Other examples include radio waves, microwaves, and X-rays. In empty space, all EM waves travel at the same speed, called the speed of light. Copyright © Houghton Mifflin Harcourt Publishing Company 7

2 main ways to transfer energy Waves can be classified by comparing the direction that they cause particles in the medium to move with the direction in which the wave moves. Copyright © Houghton Mifflin Harcourt Publishing Company 8

How do waves transfer energy? Energy can be transferred from one object to another using compressions and rarefactions. This causes energy to travel in a longitudinal wave. Compressions – the energy is close together Rarefactions-the energy is separated Sound waves travel parallel Copyright © Houghton Mifflin Harcourt Publishing Company 9

How do waves transfer energy? Energy can be transferred from one object to another using up and down motions. This causes energy to travel as a transverse wave. In a transverse wave, particles move perpendicularly to the direction the wave travels. Copyright © Houghton Mifflin Harcourt Publishing Company 10

Characteristics of waves

Crests and Troughs The points where a wave is highest are called crests. The points where a wave is lowest are called troughs. Copyright © Houghton Mifflin Harcourt Publishing Company 12

Amplitude: Distance between “rest & crest” or “rest & trough” Gives indication of “power” or “strength” of wave Does not affect velocity of wave Determines loudness (sound) or brightness (EM wave)

Wavelength: Distance between any two repeating points on a wave crest-crest, trough-trough, expansion-expansion, compression-compression Determines what colors we see; what notes we hear (pitch) Shorter wavelengths have more cycles per minute because they aren’t as long

Velocity The rate at which energy travels Depends on the medium Mechanical waves travel faster through dense mediums EM Waves are faster through less dense mediums

Frequency: number of wavelengths that pass any point per second measured in wavelengths/second or cycles/second Hertz (Hz) = number of wavelengths in 1 second Frequency is related to velocity: v = ƒ 

Period Amount of time it takes for one wavelength to pass a point Period = 1 Frequency