The How and Why of Waves

Subject Area / Grade Level / Length of Lesson
Physical Science / 6 / 3 days

Standard:

3.3.9 Demonstrate that things that make wound do so by vibrating, such as vocal chords and musical instruments.

6.3.22 Vibrations in materials set up wavelike disturbances, such as sound and earthquake waves, that spread away from the source.

Objectives:

  • Understand that sound is a form of energy that travels in waves through the air.
  • Understand and observe that sound waves and waves in general travel in all direction away from the source of a disturbance in the direction of the available medium.

Vocabulary:

  • Energy - The ability to do something (move a book, keep you warm, etc.).
  • Medium - A material (solid, liquid or gas) through which waves or disturbances travel.
  • Sound – Energy waves traveling away from a vibrating object (Vibrating air molecules).
  • Vibrate - To move rapidly back and forth.
  • Wave – A traveling disturbance that spreads away from the source of the disturbance.

Engagement

Day 1: Airzookas!

Materials:

  • Incense sticks with wooden stands (or modeling clay).
  • “Airzooka” or cardboard box replica.

Constructing a cardboard box replica of the “Airzooka” (Liem, p46)

  1. Cut a circular hole of about 15 cm diameters in the bottom of the box, and flip the flaps of the open side inwards.
  2. Staple the long rubber bands to the four corners of the side with the hole, and staple the other end of the bands to the rubber stopper.
  3. Cover the open end of the box rather loosely with the polyethylene sheet around the stopper, and tie it with a small thick rubber band.

Procedure:

  1. Begin the activity by “shooting” the students with the Airzooka or cardboard replica. Ask the students what they experience when they are “shot”. Ask the students whether they think the air that hit them in the face…
  1. Came from the air originally inside of the Airzooka and traveled across the room from the Airzooka to their face, or…
  2. The air that was right next to them was pushed into their face.
  1. Line up the incense sticks in a straight row and light them. Tell the students that as a class, you are going to perform an experiment to better understand what they just experienced with the Airzooka.
  1. Ask the students why they think that the incense sticks are being used for the experiment? If they need help, ask them what the rising smoke allows them to see (answer: the movement of the air). Explain that the rising smoke from the incense sticks allows them to observe the movement of the air surrounding it.
  • Ask the students if they have ever seen the movie Twister. Ask them if they can remember what the scientists were trying to do to better understand tornados at the end of the movie. The scientists try to drive a pickup truck full of data collecting balls into the middle of a tornado to better understand the movement of the air inside a tornado (possibly include a clip from the video). If the balls were inside the tornado, whirling around with the air, the scientists could better tell how the air was moving. The rising columns of smoke allow us to do the same thing.
  1. Ask the students what they think will happen to the rising columns of smoke if you shoot the Airzooka at them. Have them record their hypothesis on the worksheet.

Questions and Observations:(Answers should be written on the 1st page of the student worksheet)

  1. What did you see? What happened to the rising smoke from the incense sticks? (Something traveled through the air and disturbed the rising smoke but did not move the smoke across the room)
  2. What do you think caused this to happen?
  3. How did the air and smoke interact? Why didn’t the smoke rising from the incense sticks move across the room? (This will be answered during the following days’ activities, so don’t tell them!)

The smoke does not travel across the length of the room, but the disturbance caused by the stretched balloon travels across the room, interacting with each successive rising column of smoke. (Note: although this is meant to be used as an illustration of waves, what is seen traveling through the rising columns of smoke is not actually a wave as described in this activity. The sound that was produced was a wave that traveled through the air to your ear, but the visible interference was not.)

Exploration and Explanation

E

Day 2: Sound Stations

The students will cycle through a series of stations. Each station should only take a couple of minutes. Each station will demonstrate that sound is caused by a vibrating object. Provide the following directions at each station so the students can work independently. For each station, the students need to make observations and record in their science journals the answers to the following questions: (Included in the student worksheet provided)

  1. What object is making the sound?
  2. What is that object doing?
  3. What evidence did you observe to verify your answer for question two?

Station #1 Soaked!

Directions: Strike the tuning fork with the rubber hammer. Place the tips of the tuning fork into the container of water and watch out! Don’t hit the tuning fork with anything else other than the rubber hammer.

Station #2 Singing Wine Glass

Directions: Pour some water into the wine glass. Dip your finger into the water and rub it gently along the rim of the glass. Use your other hand to hold the bottom of the glass against the table. Try and make it “sing”. Be patient, it may take a little practice.

Station #3 Laser Show

Directions: Point the laser at the mirror attached to the speaker. Turn on the music and observe the reflected light from the laser on the wall or ceiling.

Station #4 Ruler

Directions: Position the ruler on the side of the table as shown in the picture. Press down on the end of the ruler, quickly release, and observe what happens.

Following Discussion: (After students complete the sound stations)

  1. Review student answers for each of the stations.
  1. Ask the students what causes sound? (vibrating objects) Is there anything that makes a sound without vibrating? (no)
  1. Discuss with the students that when objects vibrate they cause a vibration or disturbance in the air and that vibration or disturbance travels through the air to your ear. Write on the board: “a traveling disturbance is called a wave.” Sound is a wave.
  2. (Demo) Use a line of dominoes, set up on a desk, to illustrate how a sound wave travels through the air to your ear. Discuss how the disturbance (you pushing over the 1st domino) traveled across the desk, but the each domino barely moves from its original location. The disturbance could not have traveled across the desk without the presence of the dominoes or medium. (A medium is a material (solid, liquid or gas) through which waves or disturbances travel)
  1. Discuss how the students can know that sound is a wave, a moving disturbance, not just air moving from one place to another:
  • Sound obviously travels from within your throat to the all of the students’ ears because they can all hear what you are saying, but it does not take the air from your mouth with it. The sound which originated in your throat must travel through the air in you mouth in order to get to the students ears, but if it took the air with it all of the students would not only be able to hear you, but they would also be able to smell your breath, for better or worse! Since the students cannot smell your breath, unless they are in close proximity, the sound must not take your breath with it. This should illustrate that sound must also travel like the Airzooka demonstration or the dominoes, like a wave.

Elaboration

Day 2: “Where are you going?”

This portion of the activity is meant to introduce several other types of waves besides sound waves. Like the sound waves experienced the day before, students see that other types of waves are generated by the same method: vibrations or disturbances. It will also be shown that all waves spread away from the source of vibration or disturbance in the direction of the available medium.

1. Review the concepts covered in the previous portion of the activity.

  • Something can travel through the air without taking the air along with it.
  • Sound is caused by vibrations.
  • Sound is a “wave” that travels through the air.

2. Discuss with the students that waves are moving disturbances, and that these disturbances require a medium in which to travel. Air is the medium through which sound travels. (Refer back to the domino demonstration, “What is the medium in that case of the falling dominoes?”)

3. Have the students generate a list of other types of “waves” or moving disturbances (suggest the following if the students do not come up with them on their own).

  • Water waves
  • Waves on a rope / string

4. Discuss all of the student examples of waves. Discuss whether each specific example is a traveling disturbance. What is the disturbance traveling in? What is the initial cause of the disturbance?

5. Demonstrate that the following types of waves are also generated by vibrations or disturbances.

a. Demonstration 1: (water waves) Have the students stand around the clear container filled with water. Drop a single drop of food coloring into the water. Ask the students what happens to the drop of liquid when it enters the water. The students should realize that initially the coloring stays in the area where it entered the water. Now place the clear container filled with water on the over head projector. Have the students observe what happens as you allow drops of food coloring to fall into the container. This time have the students observe the projected image from the over head (the reflections and shadows due to the ripples in the water make the waves easier to see). Ask the students which direction the waves are traveling (up, down, left, or right)? The students should recognize that they don’t just travel in one direction. They travel away from the disturbance, the location where the water was dropped.

b. Demonstration 2: (waves on a rope or slinky) Tie a string to the center of a long rope or metal slinky, the longer the better. Lay the rope or long metal slinky on the floor (have a student hold one end so that it does not move). Now ask the students what they think will happen if you move one end of the rope back and forth. Proceed to quickly move the rope or slinky from one side to the next. Continue to demonstrate the creation of a wave while the students answer the following questions in their science journals.

  1. What happened when the rope (or slinky) was disturbed or quickly moved back and forth?
  2. What direction did the disturbance travel?
  1. How did the motion of the disturbance in the rope (or slinky) affect the movement of the string tied to the rope (or slinky)?

Have a second student hold the other end of the rope or long metal slinky. Now ask the students to hypothesize about what will happen if you create a disturbance in the center of the rope (or slinky).

Have the students imagine a scenario where each of them were standing in a circle facing toward the center and each of them was holding on to the end of rope which were all tied together at the center of the circle. Ask them to imagine what would happen if someone moved that center point up and down. Would waves or moving disturbances be generated? In what direction would they travel? (A moving wave or disturbance would travel out from the center, down each rope toward the students)

6. Summarize by discussing the following ideas:

  • All waves are caused by disturbances
  • Waves are actually traveling disturbances
  • Waves require a medium in which to travel (A disturbance in water will travels in water, sound waves travel in air, earthquake waves travel through the earth, etc…) Light waves are the only wave which do not require a medium in which to travel.Light waves are the only waves which can travel through the nothingness of outer space. Discuss how astronauts cannot hear anything in space. There is no matter for the sound to travel!
  • Waves spread away from the source of disturbance or vibration in the medium (in all direction if possible).
  1. Have the students look back at their written explanations about what they experienced the first day of the activity. Ask them if they can now better explain what was going on.

Evaluation / Written Assessment: “Who’s in Danger?”

A small writing project about tsunamis (seismic sea waves) will be used to assess the student’s individual comprehension of waves and their properties. Students are given some background on how tsunamis can be created. They are given a scenario which they are asked to write about. When writing the students should use what they have learned about waves and the information that they gather from the websites contained in the internet resource section.

Background Information

Tsunamis are very destructive waves that can be created by great earthquakes, underwater landslides, volcanic explosions, or meteorite impacts. Tsunamis travel at speeds up to 450 miles per hour in the deep sea and can reach heights of 50 to 100 feet once they reach the shore. While traveling through deep water their height may only be several feet. The series of diagrams to the right shows how an earthquake can cause a tsunami. (A) Shows the sea floor prior to the earthquake. (B) The earthquake causes a sudden depression in the sea floor, suddenly lowering the sea level directly above that point. (C) Water immediately surrounding the depression rushes into it trying to maintain equilibrium. The water overcompensates and creates a bulge. (D) The sea level above that point of the earthquake oscillates up and down for some time before coming to rest. These oscillations create long waves sent out in all directions over the surface of the sea. (Plummer, pp. 400-401)

References

1. Liem, Tik L. Invitations to Science Inquiry. 2nd Ed. 1992 p46

2. Plummer, Charles, David McGeary, Diane Carlson. Physical Geology. Eighth Edition. United States of America: McGraw Hill, 1999.

Authors: Christine Strattman, Ella Spreckelmyer, and Aaron Debbink

Student Information Sheet

Writing Scenario

A large meteorite is on a collision course with the earth. It is large enough to survive the passage through the atmosphere. Scientists have determined it will plunge into the Pacific Ocean several hundred miles off of the coast of Australia. They also determine it will be large enough to create tsunamis. The scientists predict that it will happen in two days. Write an imaginary article to a newspaper discussing:

  • The danger of tsunamis (why do we need be concerned about something that happens in the middle of the ocean?)
  • The places on earth that might be in danger from the tsunamis created by the meteorite impact. (Name specific countries that are in danger from this impact. Where will the waves hit?)
  • Safety precautions that should be taken

Use your knowledge of waves and the following internet sources to write your newspaper article.

Internet Resources:
1.

(PBS Online, Waves of Destruction: Tsunamis)

2.

(F.A.Q. about tsunamis)

3.

(Oregon Department of Geology and Mineral Industries, an introduction to tsunamis)

Student Worksheet

The H&W of Waves

Activity #1: Airzookas

Names______

  1. Write your hypothesis about what you think will happen when the airzooka is shot at the rising columns of smoke:

Hypothesis: ______

______

______

  1. What did you see? What happened to the rising smoke from the incense sticks?

______

______

  1. What do you think caused this to happen?

______

______

______

Activity #2: Sound Stations

Station 1 – Soaked!

Directions: Strike the tuning fork with the rubber hammer. Immediately place the tips of the tuning fork into the beaker of water.Don’t hit the tuning fork with anything else other than the rubber hammer.

  1. What object is making the sound?

______

  1. What is the object doing?

______

______

  1. What evidence did you observe to verify your answer for question 2?

______

______

______

Station 2: Singing Wine Glass