Wave Hello

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Objective

Students define a wave and apply concepts such as wavelength, frequency and velocity to wave problems.

Big Idea

The velocity of a wave can be determined by multiplying the wavelength times the frequency or by dividing the distance the wave travels by the time it takes to travel a that distance.

Context and Supplies

This lesson is an introduction to waves. Students watch a short video that defines a wave, transverse wave, longitudinal wave, wave medium and wave properties such as frequency, wavelength, velocity and amplitude.  Then in class, they witness that the speed of a wave depends on the medium and not on the amplitude or frequency as wave pulses are made on a giant slinky that students get to use. These are all key ideas for understanding wave behavior. 

This lesson incorporates NGSS Performance Standards from waves and electromagnetic radiation, HS-PS4-1: Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling in various media. NGSS Science Practice 5: Using mathematics and computational thinking is applied as is Science Practice 4: Analyzing and interpreting data, Science Practice 6: Constructing explanations (for science) and designing solutions (for engineering) and Science Practice 7: Engaging in argument from evidence as students determine that the speed of a wave is determined by the medium only. Also applied are CCSS Math Practice 1: Make sense of problems and persevere in solving them and Math Practice 2: Reason abstractly and quantitatively.

Wave Homework Quiz with Socrative

10 minutes

As students come into class, there are instructions on the board to take the Socrative quiz on Introduction to Waves (SOC #: 16393852). Most students use their smart phones and there are also laptops available. This is a six question quiz whose purpose is to give a snap-shot of how successful students were at understanding last night's Wave Introduction Homework, assigned last lesson. The homework assignment has students watch a video and learn the basics of waves, such as frequency, wavelength and velocity. The quiz is set so that Socrative.com reveals student's names and their responses as they give them (only I can see the results). I know within the first few minutes of class if there are misunderstandings that need to be addressed.  If more than 7 or 8 students make mistakes on a single question, then I review the concepts with the whole class before we move on. 

While students take the quiz, I walk around the class and record a homework grade in my grade book. Sometimes I collect and correct homework as a way to assign a grade, but since I am giving a quiz to assess student understanding, I check homework for completeness and assign a grade for effort. 

After students have completed the quiz, we review the answers as a class. I call on random students to supply the answers which I then display on my document camera.

Wave Vocabulary Lecture

10 minutes

After discuss the homework, I move onto the Waves introduction Power Point. Students should have notes about wavelength, frequency, amplitude, etc., in their notebooks from last night's homework. I inform students that most of the Power Point is review and move through it fast. However, I pause at parts where there is new information such as the definitions of wave, medium and equilibrium so that students can supplement the notes they have in their notebook with the new information. 

If a student did not do the homework the night before, they have trouble keeping up because I move fast through the Power Point. Those students complete the Wave Introduction Homework and then reference this Power Point, which I post online, to fill in all of the missing notes. I check next class to make sure they have completed this assignment.

Wave Velocity on a Slinky

25 minutes

Students now have a basic understanding of what a wave is and definitions for wave vocabulary such as medium, equilibrium, frequency, wavelength, velocity and amplitude. It's now time to play with the giant slinky! 

The purpose of this demonstration time is to let students see many of the concepts that they have been learning about. Then we finish the time with the big idea that the velocity of a wave depends only on the medium. 

I ask for two student volunteers to be the wave makers. They grab either end of the giant slinky and stretch it to about 5 or 6 meters. I let the students play around for 30 seconds or so, as the slinky is a lot of fun and the rest of the class is all smiles. I review the concepts of medium and that a wave is a disturbance that transfers energy. I then have the wave maker students demonstrate the following:

A wave pulse. A single wave going out half about a meter (which is two floor tiles in my classroom) and returning to the equilibrium position. A single pulse is the best way to measure the speed of a wave so we start there.

A transverse wave. A piece of tape is on the slinky so that students can see the coil (the medium) moves perpendicular to the direction that the wave travels.

A longitudinal wave. A piece of tape is on the slinky so that students can see the coil (the medium) moves parallel to the direction that the wave travels.

Next, I ask the other students to do a turn and talk with the following question. What could our wave maker do to change the velocity of the wave? While they discuss this, I set up my video camera to record the wave. Then I call on some students to share what they discussed. Typically, they give answers like: if the wave is made bigger, or faster or with more energy, then it might travel faster. 

So I record two waves, one small wave and one large wave. I play the video back on my computer, displaying the Wave Demonstration Video on the  projector for the class to see.  I play the video frame-by-frame so that we can conclude that the speed of the wave does not depend upon the energy or amplitude of the wave or how fast the student shook the slinky. The speed or velocity of a wave depends only upon the medium. This is an essential idea that is used throughout the unit. Here is the Unedited Wave Video.

Finally, I have the student (a.k.a. wave maker) shake the slinky back and forth about 2 times per second (2 Hz). This is a periodic wave where it is the wave source that determines the frequency. I ask a student to make an approximation on the size of the wave. About one meter is a reasonable guess. I then have the wave maker double their frequency (4 Hz). I ask another student to approximate the wavelength. It is about 1/2 a meter. The change is the wavelength is a direct consequence of the change in frequency given that the velocity of the wave does not change. I refer to the wave equation that shows this relationship.

Wave Speed Closure

5 minutes

Before students leave, I write the big ideas that they learn from the slinky demonstration on the board. Students are to write these ideas in their notebooks. 

1. The medium determines the velocity of a wave.

2. The wave source (or maker) determines the frequency of the wave.

3. The wavelength is determined by v/f.

I hand out the Wave Intro Worksheet, which is a review of everything from this lesson. I instruct the students to complete this for homework.