Introduction to Waves (Wave I)

8/11/2019 Introduction to Waves (Wave I)

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Waves I

The Basics of Waves


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The Two Main Types of Waves

Mechanical Waves are waves created bymoving matter.

ElectromagneticWaves are wavescreated by electricand magnetic fields.


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An Example of Mechanical Waves

Water waves are anexample of amechanical wave .

Other examples:Sound waves.Earthquake waves.

In a mechanical

wave , matterparticles are movingin a waving(oscillating ) motion.


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In a water wave itsthe water moleculesthat do the waving.

Actually, the wave iscaused by each watermolecule moving in acircle.


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An Example of Mechanical WavesHeres an animated example. When I start theanimation, youll be able to see the wave itself movefrom left to right.


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An Example of Mechanical WavesNow Ive highlighted one of the water molecules bycoloring it green. Watch again, and youll see themolecule simply moves in a circle.


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So although the wave itself moves forward the individual particles makingup the wave dont have an overall

forward motion.


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Transverse versus Longitudinal

Do the particles need to move in a circle? Nothey dont! Here they just move up and down.This one is called a transverse wave .


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And here they move left to right. This iscalled a longitudinal wave.


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So in transverse wave the particlesmove perpendicular to the direction thewave is moving.

Sometimes called an S wave, or a sinusoidalwave.

In a longitudinal wave the particlesmove parallel to the direction the wave ismoving.

Sometimes called a compression wave.


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Describing Waves

There are several terms in science that we useto describe a wave. To help you visualize these terms, Im going to

refer to peaks and valleys in a wave. Really,though, this is only accurate for longitudinalwaves.Speed (v) The distance through which eachwave moves every second.

Specifically the distance a peak or a valley in thewave can cover every second.


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Describing Waves

Amplitude (A) Maximum displacement ofany particle in the wave from its normalposition.


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Describing Waves

Wavelength ( ) The distance betweentwo adjacent crests (peaks) or troughs(valleys) of a waves.


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Describing Waves

Period (T) The time needed for onecomplete wave (peak to valley back topeak again) to pass by a given point.


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Describing Waves

Most of these values are actually relatedto each other.The Wave Equation:

Wave speed = (frequency)(wavelength)v =


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Describing Waves

This leads to a relationship betweenwavelength and frequency:

Wavelength = (wave speed)/(frequency) = v /

And this relationship can be reversed: Frequency = (wave speed)/(wavelength)

= v /


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Describing Waves

Finally, there is also a relationshipbetween period and frequency:

Period = 1 / (frequency)

T = 1 / Well theres also a relationship betweenwavelength and frequency, but the best

way to deal with that is to convert thewavelength to frequency and then put itinto the above equation.

Introduction to Waves (Wave I)

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