In this activity, they will be acting as cosmologists, scientists who study the structure and changes in the present universe in order to predict the future of the universe. Your role as they complete this activity is to ask questions. Allow them as much time as you consider appropriate for them to complete the activity and any follow-up explorations that may result from the activity.

As you prepare to introduce this activity, you may wish to extend your background in Cosmology and Scientific Modeling by reading the material presented in Appendix A, “Cosmology” that accompanies the Genesis Cosmic Chemistry: Cosmogony module.

The Doppler Shifts of radiation emitted by stars and other celestial objects have been used to establish that the universe is expanding between 5% and 10% every billion years. Galaxies that are 1 million light years away are moving away from us at 20 km/sec while galaxies 10 million light years away are moving at 200 km/sec, implying that the rate of expansion is uniform. These kinds of distances and velocities are difficult for most of us to envision because we have no basis for their comparison. You will again have the challenge of helping students think about astronomical distances, sizes and velocities.

Gravitational Force
Astronomers recognize the force of gravity as a major component of the universe. It has enormous influence on its structure and evolution. We all have experience with the force of Earth’s gravity attracting our bodies’ mass. When we fall, we don’t fall up. We fall toward the Earth’s surface. Gravity is a universal force that decreases with the square of the distance between two objects, so whole galaxies may move away from other galaxies, but the massive stars within those galaxies are close enough to each other that gravity is more influential than the expansion force.

• A 15 ft. long (minimum) track along which marbles can be rolled. This might be a section of 3/4 x 3/4 inch wooden corner protector (or corner molding), available in 16 ft. lengths at stores that sell lumber. Depending upon your storage capabilities, it might be better to obtain two 8 ft. sections. These sections can be connected by hot gluing 1½ inches of a 3 inch piece of curved tin to the end of one 8 ft. section. An end of the second 8 ft. then can be laid on the 1½ inches extending from the first piece. It helps to attach a board or other weight close to the end of the second piece to help the joints remain secure while the marbles are rolling down the track. Other tracks will also work, including gutter material, chalkboard trays, etc. You simply need to use something open on the top that will contain spherical objects as they roll down the track. The longer the track, the better.
  
  
• Approximately 20 marbles or other spherical objects, such as ball bearings, that are consistent with the track that you are using. Golf balls work well with a gutter and are more easily seen by visually impaired students. Golf balls in a metal gutter also provide excellent focal points for the totally blind student to follow due to the sound being produced.
  
  
• The Student Activity, “Don’t Lose Your Marbles-Are You Coming or Going?” is written as if marbles will be used. If this is not the case, advise the students of the change that you have made. Hint: In any given bag of marbles, marbles of the same size may not have the same mass. Make sure all 20 marbles weigh the same or you will introduce a variable that will change the “frequency” of the descending marbles.
  
  
• A stopwatch.
  
  
• An area where the track can be placed at waist to chest height of the students and supported on both end and elsewhere, as necessary, to keep it straight. A ring stand support attached to the upper end would be very helpful in making adjustments in height. However, if ring stands are not available, wooden blocks also work fine.
  

Stand Assembly Preparation:

1. Drill two 3/8 inch holes 8 inches apart for the post supports.
2. Sand one end of each post support dowel until it just fits smugly into the base platform.
3. In each of post support dowel, drill three 5/32 inch holes: the first hole being 1 inch from the top of the post support dowel; the second hole 1½ inches below the first; the third 1½ in below the second hole.
4. Drill a fourth 5/32 inch hole halfway between the second and third holes.

• A small tub with water for students to observe water waves.
• Audio files that correspond to high and low frequencies of sound

• A copy of the Student Text, “Are You Coming or Going?”
• A copy of the Student Text, “Doppler Shifts in the Universe”
• A copy of the Student Text, “The Gravity of the Universe”
• A copy of the Student Activity, “Don’t Lose Your Marbles—Are You Coming or Going?”
• A copy of the Student Report and Data Sheet, “Don’t Lose Your Marbles—Are You Coming or Going?”
• A copy of the Student Activity, “Gravity Simulation Activity.”

The Student Activity and Student Text materials are available for use with audio-amplified computer software, 18-point bold font print copy for partially sighted students, and in Braille for significantly sight-impaired students. You may select the most appropriate version of these materials by following these directions.

Note that there are two forms of the Student Texts and Student Activity available. One includes the phonetic pronunciation of glossary terms and is written in paragraph form for large print hard copy readers. The other is suitable for screen readers or braille transcription. It does not contain the phonetic pronunciation.

An audio tape that contains the student activity the two student texts, and glossaries is also available.

You may wish to have headsets to use with screen-reading students.

• One set of tactile cards showing sound waves. These can be obtained free of charge by downloading the PDF template here. You can then make thermally-enhanced copies for your students. Follow the directions for doing this or you may request The Dynamic Universe Tactile Card Set, which is available at cost.

1. Introduce the Doppler effect with these historical notes:

   Christian Johann Doppler, a mathematician in Prague, Austria, proposed the Doppler effect in 1842. It was his idea that a sound passing by a stationary observer will appear to change in pitch as it approaches and passes.

   In 1845, an experiment to prove the Doppler effect was carried out by Christoph Buys, a Dutch scientist, near the Dutch town of Maarsen. He used a group of perfect- pitch musicians stationed along the tracks of the Rhine Railroad as observers and arranged for a group of trumpeters to pass by on a railway car. The observers listened to trumpets being played. By noting the pitch of the notes as the train approached and receded from them, the speed of the car was accurately estimated.

2. Distribute copies of the Student Text, “Are You Coming or Going?” in the appropriate format to each student. See the Materials section for options available.
   
   
3. After students have had time to read the student text and examine the contact cards, conduct a classroom follow-up session.
   1. Have students line their contact cards up in the order 2, 1, 3 in front of them.
   2. Have them locate the lambda symbol (λ) on Card 2. Tell them that λ is the scientific symbol for wavelength. Have them observe the length of the line that extends to the left and the right of the symbol. Then have them observe that there is a crest of a wave directly beneath each end of the line. So, the length of the line is the distance from one crest to the next. This distance is called the wavelength. Have students repeat these instructions on Card 1 and Card 3. Ask what happened to the wavelength as you go from Card 2 to Card 1 to Card 3. [The answer should be that the wavelength increases.]
   3. Ask how many waves there are on Card 2. Do the same with Card One and then with Card 3. Ask what happens to the number of complete waves as you go from Card 2 to Card 1 to Card 3. [The answer should be that the number of complete waves decreases.]
   4. Now ask what relationship exists between the wavelength and the frequency of waves. [The answer should include the concept that as one increases the other decreases; this is an inverse relationship.]
      
      
4. Ask students:

1. Which card represents the frequency of a sound wave as it approaches us? [The frequency becomes higher as the sound approaches, so Card 2 would represent that.]
2. What happens to the pitch of a sound as it approaches us? [The pitch gets higher.]
3. How is the frequency of a sound wave related to the pitch of the sound? [The higher the frequency the higher pitched the sound.]
4. How is the wavelength of a sound wave related to the pitch of the sound? [The shorter the wavelength the higher pitched the sound.]
5. Which card represents the frequency of a sound wave as it moves away from us? [The frequency becomes lower as the sound approaches, so Card 3 would represent that.]
6. What happens to the pitch of the sound as it moves away from us? [The pitch gets lower.]
7. How is the frequency of a sound wave related to the pitch of the sound? [The lower the frequency the lower pitched the sound.]
8. How is the wavelength of a sound related to the pitch of the sound? [The longer the wavelength the lower pitched the sound.]

5. Distribute copies of the Student Activity Sheet, “Don’t Lose Your Marbles—Are You Coming or Going?” and the Report and Data Sheet for the student activity in the appropriate form to each student if you choose to have students do this activity in teams.

In this activity the students will observe marbles rolling down a sloped track from the source (top of the track) and calculate the “frequency” of the marbles by counting how many they collect at the end of the track during a given interval. The marbles simulate wave crests. They will determine how the “frequency” changes when they collect marbles while slowly walking toward the source and then away from the source. The activity simulates the effect of a sound receiver moving with respect to the sound.

1. You can divide the class up into teams of three and designate one team member as a “source,” another as a “timer/recorder,” and the third as a “receiver.” Alternatively, you may wish to have the class select a “source,” a “timer/recorder” and an initial “receiver” and then have each student collect his/her own data, each acting in turn as a moving receiver. In the latter case, you might also wish to rotate the “source” and “timing” responsibilities among the class so that everyone gets to collect a set of data. The exact procedure will depend on the class or how this activity fits into your schedule.
2. The “source” end of the track should be about 1 ft. higher than the “receiver” end. Students should have easy and clear access to one side of the track. Tie or otherwise clamp the track in place at the “source” end to hold the open side up. If you use wooden blocks, the track can easily be secured with hot glue.
3. It should take about 40-50 seconds to roll 20 marbles down the track when they are placed on it at roughly one-second intervals. Adjust the height of the “source” end as necessary to achieve this time frame.
4. Students should walk along the track as moving “receivers” by taking baby steps so that they cover roughly two-thirds of the length of the track in the 10 second receiving time specified. This may require them to practice a few times before collecting data. Be aware that some hand-eye coordination is required to both walk along the track slowly and pick marbles up off the track as they pass by. It may be easier for some students to use golf balls instead of marbles. With practice, even totally blind individuals can successfully complete this activity with marbles. However, golf balls do afford a better success rate. If students miss a marble and it does not get counted, they probably should start over again. The number of marbles collected while moving up and down the track does not change dramatically during the 10 second collecting period. Hence, any missed marbles can introduce significant error into the experiment.
5. Distribute copies of the Student Activity, “Don’t Lose Your Marbles-Are You Coming or Going?” and a copy of the Reporting/Data Sheet to each student.
6. Instruct the students to carry out student activity. Collect their Reporting/Data Sheets.
7. Start the next period by showing tabulated student results with the appropriate medium for your students needs. Follow up with a discussion of their observations, posing questions like the following:
   1. In what way does the “frequency” of the marbles simulate the frequency of a sound wave?
   2. How does the “frequency” of the marbles compare to the frequency of real sound waves?
   3. Can the “frequency” of the marbles be altered? Can the frequency of real sound waves be altered?
   4. How does the marble “frequency” change (higher or lower) as the receiver moves to and from the source?
   5. Why didn't all students observe the same “frequency” changes?
   6. How would the results change if the source was moving and the receiver was stationary?
   h. Instruct the students to read the Student Text, “Doppler Effect” and return their Reporting/Data Sheets to them.

6. We are now going to conduct an experiment similar to Doppler’s using a buzzer tied to the end of a rope. Do any of you have perfect pitch? [Wait for an answer. If any of your students says “yes," you might want to explore how they found out that they had this ability.] Well, it isn’t necessary for you this demonstration. [You may wish to let students examine the buzzer system tactilely before beginning the demonstration.
   
   Demonstrate the Doppler Effect using circular motion. Tell the students to form a circle well outside of the diameter of the cord. Turn on the switch inside the sock and have students listen to the pitch of the buzzer while everyone and everything is stationary. Ask students to describe what they hear. What is the pitch of the sound they hear? Does it change over a short period of time?
   
   
7. Then slowly start to swing the sock containing the buzzer around your head while letting out the cord. Try to reach the point where the buzzer is traveling around in a circle radius of 8-10 ft. at a high rate of speed. Tell the students to listen to the buzzer as you swing it in a circle.
   
   
8. Have students close their eyes* and ask the them questions like:

1. Can you tell when the buzzer is approaching you? If so, what happens to the sound of the buzzer when it is coming toward you?
2. Can you tell when the buzzer is right in front of you? If so, what happens to the sound of the buzzer at that time?
3. Can you tell when the buzzer swings on past and moves away from you? If so, what happens to the sound of the buzzer as it moves away from you?
4. (If students’ answers include only the difference in loudness, volume, or intensity, keep probing until they indicate that they hear the difference in pitch as the buzzer moves in a circle.)

9. Have students keep their eyes closed* and vary the speed of the sock. Ask the students if they can detect any difference in sound effects of the buzzer. Now tell students when you are increasing or decreasing the speed of the sock and ask:

1. What happens to the pitch of the buzzer as the speed is increased?
2. What happens as the speed is decreased?
   
   (Keep asking probing questions until students hear the rise in pitch that relates to an increase in speed and the lowering in pitch related to a decrease in speed.)

10. Ask students whether they think you, the person swinging the buzzer, can hear a change in pitch as the buzzer goes around the circle? Why or why not? [When you have heard their answers, tell them what you experienced as you swung the buzzer.]
    
    Ask if they think they would hear a change in pitch if they were to run around the circle at a speed that keeps them at the same relative distance from the swinging the buzzer? Why or why not? [If they have grasped the fact that it is the change in wavelength of sound waves as the relative velocity between themselves and the buzzer changes that is related to the change in pitch, their answer should be no. If they haven’t come to that conclusion, turn the buzzer on and have them walk with you a short distance in a straight line.]
    
    Ask if they think they would hear a change in pitch if the buzzer were in a fixed position and they were swung around in a circle in a sock? Would it depend upon where the buzzer was placed with respect to the circle? [If the buzzer were in the center of the circle in which they were being swung, there would be no change in distance between them and the buzzer. If the buzzer is in a fixed position just inside or outside the circle, then they should experience a change in pitch as they move in a circular motion. The Doppler effect would be experienced anywhere outside the circle (except directly above or below it). It is not necessary to be just outside the circle. The effect in terms of change of pitch is just the same farther away, just that the volume is of course lower.]

11. In the second section of this activity you should swing the buzzer unit in a pendulum motion so that it advances and recedes from the listener. Have students stand slightly back from either end of the arc and have them close their eyes.

1. Tell them to try to detect if the buzzer unit is approaching or receding from them. Give them a few swings of the pendulum to respond.

Have them describe what they hear as the buzzer approaches and moves away from them. [They should experience an increase in pitch as the buzzer approaches them and a decrease in pitch as it moves away from them.]

12. Gather the students together for a oral feedback and discussion that focuses on the following questions:
    1. Based on your observation and reading, how does the change in pitch as the buzzer approaches and moves away from you relate to the change in frequency of sound waves. [If the pitch of the buzzer increases as it approaches them, then the frequency of the sound waves is increasing. When the pitch of the decreases as it moves away from them, the frequency of the sound waves is decreasing.]
    2. Based on your experiences in this activity and your previous answers, what changes in pitch would you expect if the pendulum were moving faster? Explain your answer. [See the mathematical relationships in the text box.. According the formula, when v s increases, the observed frequency would increase, so the apparent pitch of the sound would increase.] What changes in pitch would you expect if the pendulum were moving slower? Explain your answer.
       
       (When v_s decreases, the observed frequency would decrease, so the apparent pitch of the sound would decrease. See the mathematical relationships in the text box.)
       
    3. Was it easier to detect a change in frequency from the buzzer going around in a circle or with the pendulum motion? Why?
       
13. Distribute copies of the Student Text “Doppler Shifts in the Universe” in the form(s) most appropriate for your students. See the “Materials” section above for options. After they have read this student text, tell students that as they were participating in these buzzer activities, they represented Earth based telescopes focused on a specific section of space. The motion of the buzzer simulated the “red and blue shift” of the stars being observed.
14. Ask if they think either the circular or pendulum motion was better than the other for illustrating red shift observed in stars and other celestial objects. [Explain that neither of them were ideal because both methods illustrated both coming and going, i.e. blue and redshifts, rather than just coming or just going, as is seen in the redshift of one star or the blueshift of another.]
15. Ask if they think either the circular or pendulum motion was better than the other for illustrating blue shift observed in stars and other celestial objects. [Use same rationale as in a. above.]
16. Ask for their ideas to use the same buzzer unit to design a better model of red and blue shifts. (This may require some time, so you may wish to make this an “out of class” assignment.)

17. Continue the “thought” session with questions similar to the following:

1. Does the Doppler effect apply to radio waves? Would a radio go “out or tune” if it were suddenly accelerated to a high velocity like that what occurs during a spacecraft launch?
2. Would a microwave oven continue to heat food if it were on a spacecraft moving at, perhaps, 2000 km/sec? (Students should realize that the source (oven) and the receiver (food) are moving at the same speed, just as is the case here on Earth. There is no change in relative velocity.)
3. If a track star were carrying a buzzer while running a 100 yard dash, would there be any perceptible change in the pitch of the buzzer as she passes by you?
4. Hydrogen has a 21 cm emission line. This is a measure of the energy that hydrogen’s photons possess. The hydrogen emission from the Andromeda galaxy can be observed on Earth. If Andromeda is moving away from Earth would its wavelength be greater or lower than 21 cm?
5. How do we use the Doppler Effect in everyday life?
6. Conclude the session by relating the importance of Doppler Shifts in the radio signals from earth to the Voyager spacecraft.
   
   

Of all the NASA missions, none has visited as many planets, rings, and satellites, nor has provided as many fresh insights into the outer planets, as Voyager, which was launched in 1977. After flying by Uranus (1986) and Neptune (1989), it left the solar system to explore interstellar space until around 2020, when the spacecraft will lack sufficient power to operate the scientific instruments on board and to return data to Earth. By then, the two Voyager spacecraft will have operated longer, and returned data from greater distances, than any previous probe. The two Voyagers have explored more planets (four), have discovered more moons (22), and have returned more photographic images, than any other space flight.

In late November 1977, while the two Voyagers were still on route to Jupiter, one of Voyager 2's two duplicate radio transmitters began to degrade. It was switched to low-power mode to nurse it along. Something was wrong, but there was no way to know exactly what. Months later, in April 1978, the Voyager team discovered that Voyager 2's backup receiver had failed to detect signals sent from Earth because of a shorted capacitor. The primary radio receiver suddenly failed completely, as well. Voyager 2 was silent. Continuing to Uranus and Neptune was no longer possible, unless a way could be found to communicate with the backup receiver.

Normally, the radio receiver automatically compensated for the Doppler shift of signals transmitted from Earth. The changing velocity and direction of the spacecraft relative to Earth caused this Doppler shift. Without the ability to compensate for the Doppler shift, the Voyager 2 radio system could not detect any signals sent to it. The solution to Voyager 2's radio problems came from NASA Deep Space Network engineers. They prepared computer tapes that slowly varied the frequency of the radio signals transmitted from Earth in order to compensate for the expected Doppler shift. The Deep Space Network station outside Madrid transmitted the first test signals on April 13, 1978. Fifty-three minutes later, Voyager 2's acknowledgement returned. The trick worked. As a backup measure, in October 1978, Voyager 2's memory banks were loaded to the brim with commands that would provide for a bare-minimum science encounter at both Jupiter and Saturn, should radio contact once again be lost. The same procedure was followed for subsequent encounters at Uranus and Neptune.

The above are excepts from http://history.nasa.gov/SP-4219/Chapter11.html, where you may find more complete background material.

1. Distribute copies of the Student Text “The Gravity of the Universe” in the form(s) most appropriate for your students. See the Materials section above for options. Give students ample time to read the Student Text or assign it as homework for the next class.
2. Distribute copies of the Student Activity, “Gravity Simulation Activity” in the form(s) most appropriate for your students.
3. Allow students sufficient time to complete the activity and answer the questions. If none of your students have any sight, you may need to help your students manipulate the horizontal supports and magnets.
4. As background for this discussion, you will probably want to read the following materials from the original Cosmic Chemistry: Cosmogony materials: Teacher Guide: Cosmic Tug of War and the Student Text: Cosmic Tug of War. During a follow-up session, ask any of the following questions that you think are appropriate for you students:
   1. Why would we not expect any Doppler shifts in atmospheric emissions of the planets of the solar system as observed from earth?
   2. Consider two spherical objects that are attracted to each other gravitationally with X amount of force. If the distance between the objects is tripled, will the new force of gravitational attraction be greater than X, less than X, or the same as the original X force? (Increasing the distance between the objects will decrease the gravitational force, since the gravitational force between two objects is directly proportional to the masses of the objects and inversely proportional to the square of the distance between them. See formula in box.)
5. Now consider the scenario in which the same two objects with X amount of gravitational attraction are replaced with the two objects having a mass five the times that of the original objects. These new objects are the same distance apart as the original objects. Would the gravitational force between the new objects be greater than X, less than X, or the same as the original X force?? (Increasing the mass of the two objects increases the gravitational attraction, since the gravitational force between two objects is directly proportional to the masses of the objects and inversely proportional to the square of the distance between them. See formula in box.)

• What do you think would be happening to the size of the solar system if there were no gravitational force between the planets and the Sun?
• What do you think would be happening to the distance between the Andromeda galaxy and the Milky Way galaxy if there were no attractive force operating between them?

6. Complete this module of study by reading the following Basic Precepts of the Standard Cosmological Model for your students:
   1. The physical laws that we experience on Earth pertain throughout the observable universe.
   2. The universe is expanding
   3. The universe is isotropic and homogenous.
   4. General relativity (Einstein’s theory that incorporates Newton ’s) accurately describes the behavior of gravity in the universe today.
   5. The universe is evolving.

   All of these model precepts are written in the present tense. Ask why students think this is so. (Because all of them pertain to the universe as it is today.)

   There are two of these precepts—those describing gravity and expansion—that involve forces that are in opposition to each other. Ask how might these two opposing forces make for a universal “tug of war.” (Think about a rope “tug of war.” What happens when one side gets a little “edge” on the other. What happens when one side wins?)

   Ask how these opposing forces make for a dynamic, rather than a static universe. (What would happen if neither side ever won?)

   Ask students to predict what might happen to the universe in the future. Do they think the universe will continue to expand? Will it expand for a while and then stop? Are the gravitational forces large enough to eventually make the universe contract? What would we need to know so that we could make more accurate predictions?