Focus: Waves
Objective: Compare the properties of waves tothe wavelike property of energy in earthquakes,light and sound.
EQ: What are the 2 kinds of mechanicalwaves? How are they similar? How arethey different?
WAVES
Vocabulary to Know
What is awave?What is awave?
A wave is a type ofenergy.A wave is a type ofenergy.
Waves transferenergy not matter.Waves transferenergy not matter.
Examples:Examples:
In the OceanIn the Clouds EarthquakeIn the OceanIn the Clouds Earthquake
The water waves below are carrying energy but are notmoving. Waves can only exist as they have energy tocarry.
Waves are started by a force. Let’s look at a slinky. Whenyou shake a slinky, it creates a wave. In this case, wecreated a force by moving the slinky.
Waves move away from the force.
ForceForce
Direction of the waveDirection of the wave
When a force creates a wave, energy moves not matter. The forcemakes the atoms in the matter vibrate. The vibration causes them tobump into each other like dominoes, sending the wave down the line.But the matter itself stays in the same spot.
Let’s try it!
What are mechanical waves?
Mechanical waves travel through a medium. A medium is a kind ofmatter like water, air, or glass.
What are the two kinds of mechanical waves?
Transverse Waves
In a transverse wave the matter in the wave movesup and down at a right angle to the direction of thewave.
Transverse Waves:Transverse Waves:
In a transverse wave the matter in the wavemoves up and down at a right angle(perpendicular) to the direction of thewave
The wave is moving away from the force.The wave is moving away from the force.
The energy is moving up and down, perpendicular to thewave’s direction.The energy is moving up and down, perpendicular to thewave’s direction.
•Which direction is the energy in the wave going?
[ (away from the moving hand) / (toward the moving hand) ]
•How can you tell?_______________________________________________________
•What is the medium for this wave?__________________________________________
•Which direction is the mediummoving?_______________________________________
•What type of wave is this?_________________________________________________
SHOW WHAT YOU KNOW:SHOW WHAT YOU KNOW:
Example of a transverse wave:
Give me the gist.
• In your interactive notebook, write a definitionof a transverse wave is in 20 words or less.
What is the second kind of mechanical wave?
Longitudinal Waves (Compression Waves)
In a longitudinal wave the matter in the wave movesback and forth parallel to the direction of the wave
In a longitudinal wave the matter in the wavemoves back and forth parallel to the direction ofthe wave
The energy moves in the same direction as the wave.
Sound waves are longitudinal.
Longitudinal waves
Transverse waves
•Which direction is the energy in the wave going?
[ (away from the moving hand) / (toward the moving hand) ]
•How can you tell?_______________________________________________________
•What is the medium for this wave?__________________________________________
•Which direction is the mediummoving?_______________________________________
•What type of wave is this?_________________________________________________
•Compared to the direction of the energy, the medium moved in what direction?__________________________________________________________
SHOW WHAT YOU KNOW:SHOW WHAT YOU KNOW:
Gist of a longitudinal wave.
•Think-pair-share
•Share out
Seismic waves are what we call the wavesthat happen during an earthquake.
•When an earthquake happens, energy wavesvibrates through the earth’s crust as the crustbends or breaks.
During an earthquake, there areboth:
•Transverse waves
•Longitudinal waves
Which wave travels faster?
Think-Pair-Share:
•Think about the slinky
•Let’s find out!
–Human wave activity
Since the energy is traveling the fastest way it can (in a straightline), the longitudinal wave is faster than the transverse wave. Itgets from the force to the stopping point first. It is the first wave youfeel in an earthquake.
The transverse wave takes more time and energy to goperpendicular to the direction of the wave. You feel this wavesecond in an earthquake. It is sometimes called the “aftershock”.
Which wave does moredamage?
Think-Pair-Share:
Write the questions and answerthem in your interactive notebook.
1.Which wave do youthink would do moredamage to a city?
2.Why do you think so?
•Let’s find out!
–Human wave activitywith buildings
What are the parts of a wave?
Transverse wave
The crest is the highest point on a transversewave. The trough is the lowest point on atransverse wave.
The rest position of the wave is called the nodeor nodal line.
What do we callthe tops andbottoms ofwaves?
The top of the wave is the CREST.
The bottom of the wave is theTROUGH.
Vocabulary to Know
CRESTCREST
TROUGHTROUGH
What are the parts of a wave?
Transverse wave
The wavelength is the distance from onepoint on the wave to the same point on thenext wave.
Compressional
Longitudinal wave
On a compressional wavethe area squeezedtogether is called thecompression. The areasspread out are called therarefaction.
The wavelength is thedistance from the center ofone compression to thecenter of the nextcompression.
The amplitude of a transverse wave is determined bythe height of the crest or depth of the trough
What isamplitude?What isamplitude?
Amplitude is the height of thewave. It is how high and howlow the waves go.Amplitude is the height of thewave. It is how high and howlow the waves go.
Vocabulary to Know
How highdoes it go?How highdoes it go?
How lowdoes it go?How lowdoes it go?
What is wavelength?
Wavelength is a measure of distance, so the units forwavelength are always distance units, such as meter,centimeters, millimeters, etc.
What is wave frequency?
Frequency is the number of waves that pass through apoint in one second. The unit for frequency is waves persecond or Hertz (Hz). One Hz = One wave per second.
Wavelength and frequency are inversely related.
The smaller the wavelength, the more times it will pass through apoint in one second. The larger the wavelength, the fewer times itwill pass through a point in one second.
What isfrequency?What isfrequency?
Frequency is the number ofcrests OR troughs in a givenspace or time.Frequency is the number ofcrests OR troughs in a givenspace or time.
Vocabulary to Know
How many troughs?How many troughs?
How many crests?How many crests?
33
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Waves have measurableproperties
Frequency is the number of waves(vibrations) that pass through a point in onesecond.
Period is the time it takes for one fullwavelength to pass a certain point.
Frequency is waves per second.
Period is seconds per wave.
A wave moving through a medium travels at a certainspeed. This is Wave Speed.
Wave speed is usually measured in meters/second, butmay be measured using other distance units (such ascentimeters per second).
How is Wave Speed calculated?
Wave speed is calculated as the product of a wavesfrequency and wavelength.
Wavelength is represented by the Greek letter lambda(λ) and frequency is represented by (f)
