Properties of Waves: Making Waves Visible

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Objective

Students will be able to identify that there are various types of waves with properties that are similar and different, identify properties of waves and create models that demonstrate relationships.

Big Idea

Wave properties need to be visible to students to promote understanding. Use tuning forks, rope springs, and slinkies to model waves and their properties!

Introduction and Connection to the NGSS

This lesson is the introductory lesson for the students and is a lesson that takes place over the course of 2 days.  Waves can be a challenging topic for a middle school student.  With many waves being "invisible", it can be difficult for a student to relate to and explain.  As a result, they have many misconceptions about wave behavior.  In order to allow students to make connections, this lesson helps make wave properties visible.  The Next Generation Science Standards have identified an essential question that can drive student learning in "What are the characteristic properties of waves and how can they be used?"  This lesson focuses specifically on the following NGSS standard:

MS-PS4-1 Use mathematical representations that describes a simple model for waves that includes how the amplitude of a wave is related to the energy in the wave.

The disciplinary core idea PS4-A explains that a simple wave has a repeating pattern with a specific frequency, wavelength, and amplitude.  In turn, creating relationships between these wave properties is critical for student understanding.  Graphs and charts are a great method for representing patterns in data mathematically.  With the use of slinkies, students can discover these relationships and gather data for developing their own graphs showing property relationships.

Materials Required:

Slinkies (1 per group)

Rope Springs (1 per group)

Beaker or shallow dish (1 per group)

Tuning Fork (2 of different sizes per group)

Connection to the Essential Question: What am I going to learn today?

5 minutes

Provide students with the Unit Plan that includes the Essential Question, "What are the characteristic properties of waves and how are they used?" along with the "I can" statements/skills for the unit.  Read the EQ as a class and break down what the question might be asking.  For example, ask students what "characteristic", "properties", and "how are they used" might mean.  Many middle school students have an especially difficult time verbalizing what a property is.  Without this understanding, it will be challenging for them to connect to what they are supposed to be learning.  A conversation may unfold something like this:

Teacher:  What does the word characteristic mean?  Your response does not have to be connected to science.  In your everyday life when you hear that word, what does it mean to you?

Student:  Something that describes something

Teacher:  Absolutely!  One characteristic about me is that I love science.  What does the word property mean to you?  Again, your response does not have to be connected to science.  In your everyday life when you hear the word property, what does it mean to you?

Student:  Something you own, something that is yours

Teacher:  Absolutely!  Now, I am wondering how a wave can own something.  What is it that a wave can own?

Student:  Like what type of wave it is or what it looks like

Teacher:  Hmmm....characteristic and property both seem like they mean similar things.  They are both words that make us think of descriptions of things.  I wonder why both words are in this Essential Question.  (Pause....Wait time!  Let the students think about why both words are needed.)  Let me ask you this.  I notice that in this question the word characteristic is used a little differently.  It says, "characteristic properties".  I wonder how the meaning of the word characteristic changes when it is put in front of another word like this.  For example, what if I said, "What are the characteristic properties of a science teacher?"  What does the word characteristic mean now?

Student:  typical or common

Teacher:  Ahh!  That makes sense.  So, what we are looking for here it seems is typical or common ways to describe waves.  Maybe it is the things that waves might have in common. 

Teacher:  I am noticing that there is a second part to this EQ.  It mentions, "how can they be used".  What do you think we should look for when making connections to that?

Student:  Maybe...ways that humans might use them in the real world

Once the class has an understanding of the EQ, have students close their eyes and picture as many waves as they can in 20 seconds.  Ask students to share what images came to their heads about what a wave looks like.  Often students mention water waves, earthquakes, sound, light, or a line that goes up and down.  Many of them demonstrate with their hands or fingers and draw a curvy line.  Recognizing that there are many types of waves is a key concept here.  Let this lead into a discussion that there are a variety of types of waves and each of them have their own properties.  Students should recognize that some of these properties are the same for all waves; however, some ways that waves interact with matter and the way they are caused can vary.

Have students look at Skill 2 and Skill 3 in the Unit Plan and tell them this will be the focus for the next days.  Have them rank their level of learning with each of the two skills on a scale of 1 to 4 (4 being mastery) on their Unit Plan.  Then, ask them to underline the key vocabulary that they are going to try to connect to in the lesson and circle the verbs that explain what they will have to do with that vocabulary.  Ask students to share the vocabulary they identified such as amplitude, frequency, wavelength, and pitch.  Then have them identify what they have to know about these terms.  I often ask, "Do you just have to define them?  What do you have to do to demonstrate mastery?"  Students say things like create models, find the relationship between them, and provide evidence of the relationships.  

Before beginning the mini lesson, ask students to raise their hand and share with the class if they make a connection to one of the skills during instruction.  If students share their connections, it will help other students make connections as well.  For example, if at some point in the lesson I mention the word "frequency" (one of the words that they underlined), a student should raise their hand and say, "I made a connection to Skill 2! This must be an important property of waves!"  I also invite students to use the skills to ask questions at this point.  For example, at the point that I say "frequency", a student might raise their hand and say, "I just connected to Skill 3.  What would be a situation in the real world that provide evidence of it?".  Share examples like this with students so that they have a frame of reference of what your expectations are.

Mini Lesson

15 minutes

Now that the students have shared their vision of what a wave looks like, ask them what a wave actually is and allow for suggestions.  Explain to the students that a wave is a disturbance that transfers energy from one place to another.  Emphasize to students that waves transfer energy, not matter.  This is a very important conceptual picture that students need to grasp.

Ask a group of students (6 - 7) to come to the front of the classroom and stand in a horizontal line shoulder to shoulder facing the class.  Stand next to the first person in the line and explain that you and the students are going to do the wave (like at a sporting event).  Demonstrate the wave and say, "Waves transfer energy, not matter."  Then, demonstrate again.  Explain that you are going to show something that does not happen with waves.  You start the wave and as the wave moves, run to the end of the line (So, you are the start and also the finish.).  Ask the class how a wave at a sporting event works. Do the people participating run all around the stadium? Or does the wave "transfer" from person-to-person. Connect to the idea that waves in the world operate similarly in that they do not transfer matter either.  They simply transfer energy.

Next, ask students to picture an ocean wave.  It begins far out in the ocean and those that move toward the shore break as they strike the shoreline.  I have the students close their eyes and picture the most peaceful ocean beach.  I have them follow the wave from out in the ocean to the shore.  I have them try to hear the wave break on the beach.  Then I say, "Continue to keep your eyes closed...how many of you are picturing the water in the middle of the ocean that started the wave moving with the wave and landing on the shore of the beach?"  Many students raise their hands.  A great number of students have the misconception that the water from the middle of the ocean travels all the way to shore.  Explain that this is not the case.  Again state, "A wave transfers energy, NOT matter."  While energy is transferred from the middle of the ocean to the shore, the matter is not.  Explain that instead, that water wave is transferring through the matter and that the matter that a wave travels through is called a medium.  In an ocean wave, energy transfers through the medium of water.

In the upcoming demonstrations, students will communicate their learning on the Introduction to Waves Notes Page which already includes the definitions of wave and medium.  I have also included a filled in Teacher Notes Page (answer key) that leads me through the rest of the lesson.

Student Demonstrations

20 minutes

Now that students have a visual of what a wave looks like, a working definition of what a wave is, and an initial idea about how waves move, explain to students that they will be completing a couple of demonstrations in order to help identify some properties that different types of waves have.  Hopefully, a student's hand shoots up and they say, "I just connected to the essential question!".  If they don't, help students recognize that this is a moment to make a connection.  Sometimes I even take a student seat and have a student stand up and give the directions.  For example, I may have a student say, "Complete the demonstrations and look for properties of waves."  I then (sitting in a student desk) raise my hand as a student would and say, "I notice you just said the word 'property'.  I tuned in immediately because it is the focus of the EQ."  Without practice and teaching of how to connect to the Essential Question and skills, students will not make the connections they need.

Demonstration 1:  Rope Wave Demonstration

Have students use a rope spring to create various waves of their choice.  Ask them to start to look for characteristics and properties of the waves they create.  In addition, ask them to note medium, the direction of the disturbance as well as the direction the wave is traveling.  

Rope springs are long and take up a lot of room.  If it is nice outside and you have a close exit, I like to take the students outside here.   When students are finished demonstrating (5 minutes) have them complete the Rope Wave Demonstration section on the Introduction to Waves Notes page labeling the focus named in the question.  Discuss each of the foci as a class.


Demonstration 2:  Water Wave Demonstration

Next, students demonstrate water waves with the same purpose as the Rope Wave.  Using tuning forks, have the students hit the fork on the edge of the table and then lower the vibrating fork into the water.  In addition to noting the medium, the direction of the disturbance as well as the direction the wave is traveling, have the students note if there is any difference or relationships in energy transfer with the different tuning forks.  

Water will spray!  Students love this, but it will get their papers wet.  I have them perform this at a lab counter away from their personal work space.  When students are finished demonstrating (5 minutes) have them complete the Water Wave Demonstration section on the Introduction to Waves Notes page labeling the foci named in the question.  Discuss each of the foci as a class.

Next, discuss the Earthquake Model included in the Introduction to Waves Notes page.  Have students identify the medium, direction of disturbance, and direction of the wave for seismic waves. 

Demonstration 3:  Transverse Vs Longitudinal Waves

Explain that various waves behave differently from one another.  For example, transverse waves (like light and electromagnetic radiation) are waves that move perpendicular to their disturbance while longitudinal waves (like sound waves) move in the same direction as their disturbance.  Have the students fill this in on their notes sheet.  

Provide each group with a slinky.  Ask them to use the slinky to create a model of the definitions of transverse and longitudinal waves that you just discussed.  As tempting as it is, give them no hints. Students must use the words in the definition to create their own understanding with the slinky. Check in with each group to see if they have developed appropriate models.  Transverse waves can be created by moving their hands side to side or back and forth.  Longitudinal waves are created when the students push the slinky forward on the ground towards a classmate at the other end of the slinky causing compressions in the slinky.  Have students draw their model on their Introduction to Waves Notes page.

I have included the teacher page with possible answers as well.

Student Modeling and Formative Assessment With Slinkies

30 minutes

Draw a transverse and longitudinal wave on the board.  Label and explain each of the following characteristics of waves: crest, trough, amplitude, frequency, wavelength, and pitch.

Next, have students use the slinkies on the floor (I find if they are off the ground, slinkies tangle more often) to model and identify each aspect for about 5 minutes.  During this time, walk from group to group and ask, "Where is the crest?  The trough?", "How can measure a wavelength?", "How can you show frequency?", etc.

Then, ask them to see if they can determine if there is a relationship between frequency and wavelength.  Check in with each group to see if they have developed the correct relationship model.  Students should find that an increase in frequency results in a decrease in wavelength. For any group that is struggling, ask them, "What does the word 'frequency' mean to you?  With what word do you relate it with?"  Many students say something like, "Speed".  I might say, "Ok.  That means we need to pay attention to what about the wave changes when you move the slinky fast and then slow. Why don't you try that?  What about the wave changes?".  Students often say, "There are more waves when I move it fast."  After this, I ask the student to review what a wavelength is.  Once they have the idea that a wave length is the distance from crest to crest, I ask, "If wavelength is the distance from crest to crest, does this distance increase or decrease when you move the slinky faster?"

Below is a video of a group of students discovering the relationship between frequency and wavelength.  Notice that they are describing evidence of the relationship using appropriate science vocabulary.

Then, lead the groups through a series of models.  These may take anywhere from 1 minute to 3 minutes each, depending on where the students are in their mastery.  Typically, as the students gain understanding, each model can be completed fairly quickly.

Ask the students to model the following:

1.  Longitudinal wave with a high amplitude.

2.  Longitudinal wave with a low amplitude.

After the first two models, ask the students to verbalize what they have to do to create longitudinal waves.  Students might say, "We push the slinky instead of moving it side to side."  Then, ask the same for amplitude.  Students might say, "We push the slinky harder for high amplitude and softer for low amplitude."

3.  Transverse wave with a high amplitude.

4.  Transverse wave with a low amplitude.

After these models, stop the class and ask students to verbalize what they have to do to the slinky to make a transverse wave.  Students might say, "We move the slinky side to side."  Then say, "A wave that has a high frequency has what we call a high pitch.  For sound, that means a sound like this 'eek!".  A wave with a low frequency, has a low pitch.  For sound, that means a sound like this 'boom!." 

5.  Longitudinal wave with a high pitch.

6.  Transverse wave with a low pitch.

Following these models, ask the students to verbalize what they had to do in order to create a high pitch with a slinky.  A student might say, "Either push it fast or move side to side fast."  Confirm that idea and connect to frequency.  I might say, "Absolutely!  High pitches are tied to high frequencies.  A high frequency wave does have a higher pitch.  Frequency and pitch are directly proportional.  That means that as frequency increases, pitch also increases."  While explaining directly proportional, I use my thumbs.  When I say, "as frequency increases", I put my right thumb up.  When I say, "pitch also increases", I put my left thumb up while leaving my right thumb still up.  I often repeat this statement and motion so students can connect to direct proportionality with a physical movement.

7.  Transverse wave with a short wavelength.

8.  Longitudinal wave with a high frequency.

Following these models, ask the students to verbalize what they had to do in order to create a short wavelength.  Students might say, "Move it side to side fast."  Confirm that idea and connect to frequency.  I might say, "Absolutely!  Short wavelengths are tied to high frequencies.  A high frequency wave does have a shorter wavelength.  Frequency and pitch are inversely proportional.  That means that as frequency increases, wavelength decreases."  While explaining inversely proportional, I use my thumbs.  When I say, "as frequency increases", I put my right thumb up.  When I say, "wavelength decreases", I put my left thumb down while leaving my right thumb still up.  I often repeat this statement and motion so students can connect to inverse proportionality with a physical movement.

Then, increase the complexity:

1.  Longitudinal, high pitch, high amplitude

2.  Transverse, low frequency, high amplitude

3.  Transverse, high frequency, low amplitude

4.  Longitudinal, long wavelength, low amplitude

These students start to demonstrate some understanding during this modeling activity.  Students start to realize that transverse means moving their hands side to side while longitudinal means pushing the slinky forward, that high amplitude with a transverse wave means moving their hand a larger distance side to side while a high amplitude in a longitudinal wave means pushing the slinky forward hard, and that a high frequency and high pitch means moving the slinky at a faster rate.

Closure

5 minutes

Have students put slinkies away and return to their seat.  Ask students to look at Skills 2 and 3 on the Unit Plan and rank themselves again on a scale from 1 to 4.  Did their level of mastery increase from the beginning of the lesson to the end of the lesson?

Then, ask students to show the following using their hands as if they were holding the slinky.  Ask, how would you move your hand to create....

1.  Longitudinal wave - students should push their hands forward.

2.  Transverse wave - students should move their hands back and forth.

3.  High amplitude for a Longitudinal Wave - students should push hard

4.  Low amplitude for a Longitudinal Wave - students should push soft

5.  High amplitude for a Transverse Wave - students should move their hands back and forth a large distance

6.  Low amplitude for a Transverse Wave - students should move their hands back and forth a small distance

7.  High frequency for a Longitudinal Wave - students should push their hands fast

8.  Low frequency for a Transverse Wave - students should move their hands back and forth slow

9.  Long wavelength for a Longitudinal Wave - students should push their hands slow

10.  Short wavelength for a Transverse Wave - students should move their hands back and forth fast

A really important distinction to emphasize as students have misconceptions is that amplitude is independent of frequency.  Students quickly confuse energy with speed.  They believe that more energy means you have to move fast.  However, you can have a low pitch sound with a high amplitude.  Anytime you notice a student correlating frequency and amplitude, correct their misconception.