Focus: Waves

Objective: Compare the properties of waves to the wavelike property of energy in earthquakes,

light and sound.EQ: What are the 2 kinds of mechanical

waves? How are they similar? How are they different?

WAVES

Vocabulary to Know

What is What is a a wavewave??

A wave is a A wave is a type of type of energy.energy.Waves transfer Waves transfer energy energy notnot matter.matter.Examples:Examples:

In the OceanIn the Ocean In the CloudsIn the Clouds Earthquake Earthquake

The water waves below are carrying energy but are not moving. Waves can only exist as they have energy to carry.

Waves are started by a force. Let’s look at a slinky. When you shake a slinky, it creates a wave. In this case, we created 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 force makes the atoms in the matter vibrate. The vibration causes them to bump 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 of matter like water, air, or glass.

What are the two kinds of mechanical waves?

Transverse Waves

In a transverse wave the matter in the wave moves up and down at a right angle to the direction of the

wave.

Transverse Waves:Transverse Waves:

In a transverse wave the matter in the wave moves up and down at a right angle (perpendicular) to the direction of the wave

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 the The energy is moving up and down, perpendicular to the wave’s direction.wave’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 medium moving?_______________________________________

•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 definition of 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 moves back and forth parallel to the direction of the wave

In a longitudinal wave the matter in the wave moves back and forth parallel to the direction of

the 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 medium moving?_______________________________________•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 waves that happen during an earthquake.

• When an earthquake happens, energy waves vibrates through the earth’s crust as the crust bends or breaks.

During an earthquake, there are both:

• 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 straight line), the longitudinal wave is faster than the transverse wave. It gets from the force to the stopping point first. It is the first wave you feel in an earthquake.

The transverse wave takes more time and energy to go perpendicular to the direction of the wave. You feel this wave second in an earthquake. It is sometimes called the “aftershock”.

Which wave does more damage?

Think-Pair-Share:Write the questions and answer

them in your interactive notebook.

1.Which wave do you think would do more damage to a city?

2.Why do you think so?

• Let’s find out!– Human wave activity

with buildings

What are the parts of a wave?Transverse wave

The crest is the highest point on a transverse wave. The trough is the lowest point on a transverse wave.

The rest position of the wave is called the node or nodal line.

What do we call the tops and bottoms of waves?

The top of the wave is the CREST. The bottom of the wave is the TROUGH.

Vocabulary to Know

CRESTCREST

TROUGHTROUGH

What are the parts of a wave?Transverse wave

The wavelength is the distance from one point on the wave to the same point on the next wave.

Compressional Longitudinal wave

On a compressional wave the area squeezed together is called the compression. The areas spread out are called the rarefaction.

The wavelength is the distance from the center of one compression to the center of the next compression.

The amplitude of a transverse wave is determined by the height of the crest or depth of the trough

What is What is amplitudeamplitude??

Amplitude is the height Amplitude is the height of the wave. It is how of the wave. It is how high and how low the high and how low the waves go.waves go.

Vocabulary to Know

How high

How high

does it does it

go?go?

How low

How low does it does it go?go?

What is wavelength?

Wavelength is a measure of distance, so the units for wavelength are always distance units, such as meter, centimeters, millimeters, etc.

What is wave frequency?

Frequency is the number of waves that pass through a point in one second. The unit for frequency is waves per second 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 a point in one second. The larger the wavelength, the fewer times it will pass through a point in one second.

What is What is frequencyfrequency??

Frequency is the number Frequency is the number of of crests OR troughscrests OR troughs in in a given a given spacespace or or time.time.

Vocabulary to Know

How many How many troughs?troughs?http://id.mind.net/~zona/mstm/physics/waves/introduction/introductionWaves.html

How many How many crests?crests?

33

33

Waves have measurable properties

Tf

periodfrequency

11

Frequency is the number of waves (vibrations) that pass through a point in one second.

Period is the time it takes for one full wavelength to pass a certain point.

Frequency is waves per second.

Period is seconds per wave.

A wave moving through a medium travels at a certain speed. This is Wave Speed.

Wave speed is usually measured in meters/second, but may be measured using other distance units (such as centimeters per second).

How is Wave Speed calculated?

Wave speed is calculated as the product of a waves frequency and wavelength.

Wavelength is represented by the Greek letter lambda (λ) and frequency is represented by (f)