Divide Class Into Groups of 3-4 Students

Doppler Effect Activities:

Divide class into groups of 3-4 students.  Give each group 1 tray and 1 eyedropper.  Put about 1/4 or 3/8 inch of water in each tray.  Have students use the eye dropper to drop water in the tray at regular intervals (eye dropper to remain stationary.)  Have students draw their observations.  Have students move the eye dropper (source of wave making) while dropping the water.  Have students draw their observations. Demonstration:  Place the flat-bottom dish on an overhead and produce waves by squeezing drops of water out of the dropper at regular intervals.  This should produce waves of the same wave length.  Continue to make waves while moving the source toward one end of the dish.  These are examples of questions and discussion that this activity should draw out:  Define wave length, crest, trough, frequency.  Notice that the wave lengths are the same at both ends of the dish as the source of the waves stays stationary.  Notice that as the source moves, the waves are being produced at the same rate and travel at the same speed. Have students draw their observations on the worksheet. (Wave lengths should be shorter in the direction of the source and longer on the other end of the tank.)

 Have students stand around the outside of the room while the teacher swings the noise maker around on the string. Ask students to raise their hands when they notice a change in pitch (frequency).  (Students should note that the pitch of the noisemaker changes.) Have students share their observations and come to a consensus about what they heard.  These are examples of questions and discussion that this activity should draw out:  Relate the water waves to sound waves.  The source of waves always produces waves at the same rate and the waves travel at the same speed.  Notice that the waves "bunch up" or "spread out" depending upon the direction the source is moving.  Moving the source results in higher or lower pich of the sound. Can you change the pitch without moving the source? (Yes.) How? (Move the observer.)  Use a slinky or spring to demonstrate waves being bunched up and spread apart (high frequency and low frequency)  These are examples of questions and discussion that this activity should draw out:  Light travels in waves.  Colors of light are related to wave length.  (Show a chart of the spectrum of light that shows colors.) Relate how pitch and color are determined by wavelength.  Relate doppler effect with red shift of stars a - what questions and discussion should draw out:  Each edge of the sun gives a shift: one red and one blue.  The side with a blue shift is moving towards us while the side with a red shift is moving away from us.  This is one way we know the sun rotates.  Ask students: how would we know if stars are moving away from us or towards us?  (answer- away- red shift low frequency; towards- blue shift high frequency)  Ask students: if several stars are moving away from us could we determine if one is moving faster away from us than another? Can we tell if we are moving away from the star or is it moving away from us?  (answer-the faster the stars are moving away the more the red shift.  *Discuss relative motion- the source can be moving or the observer can be moving or both the source and the observer can be moving.