An approach to the Doppler Effect by Gonzalo Loureiro Graduate in Mathematics

Introductory section and preparatory phase Short Description: The scope of this Educational Pathway is to learn about the nature of sound (specifically pitch and what it depends on) and explain the Doppler effect informally using Science Center to Go materials. Keywords: waves, sound, pitch, frequency, relative speed, speed of sound, stationary, concentric circles, light, speed of light, redshift phenomenon. Target audience: secondary students Age range: Context: physics, kinematics.

Technical Requirements: Science Center to Go suitcase (a laptop computer, a webcam and five small-scale centre exhibits (miniatures), specifically the Mini-fire truck (to learn about the Doppler effect) Connection with the curriculum: as a prerequisite, the students should be familiar with the wave nature of sound and know the basics about kinematics Learning Objectives: get deeper into the nature of sound, explain phenomena via observation and description, relate previous knowledge of kinematics with new phenomena. The goal is not to derive difficult equations related to the Doppler Effect, but understand the phenomenon better and prepare for doing so in the next courses. Guidance for preparation: the teacher should get familiar with the Science Center to Go project and its goals, and learn how to use the Science Center to Go materials by reading the user's manual. A certain amount of self-training and testing is recommendable before implementing the pathway in the class. Introductory section and preparatory phase

Science Centers and Museums offer intriguing exhibits that enable their visitors to experience science first hand by actively manipulating the experiments, thus delivering natural ways of active playful learning. Modern technologies like Augmented Reality (AR) are often used to enrich the experience and display otherwise hidden phenomena. However, experiencing AR requires visiting the Science Center or Museum. Description of Science Center to Go

The SCeTGo approach goes one step further and aims to bring similar comprehensive learning experiences out of the SC into a school's classroom and/or everyone's home. Its miniature exhibits - by "fitting into a pocket" and operating with ordinary hardware enable learners to experiment whenever and wherever they please. Description of Science Center to Go

The miniature is set up in the webcam's field of view. The webcam transmits an image to the lapton screen. The software adds an overlay to the image. The overlay depicts an aspect of the scientific phenomenon under investigation. This process of adding unseen elements to the image on the screen is Augmented Reality (AR) The activity for the users could be to work out how to use the miniatures and guess or deduce what they are showing, rather than follow instructions. Learners have the oportunity to realise that the best way to make investigations is to make one change at a time and make careful observations Description of Science Center to Go

Teaching Phase 1: Question Eliciting Activities PROVOKE CURIOSITY In the begining, the teacher will project very informal videos about phenomena depicting the Doppler effect, so that pupils get motivation and get encouraged to make themselves questions about the phenomenon. This videos depict: -The sound of a firetruck passing by: -The sound of a motorbike passing by -The sound of a car horn as the car passes by A general discussion on the topic is recommended, even if the pupil's answers are spontaneous and, in the beginning, not related to a scientifical background

Teaching Phase 1: Questions Eliciting Activities DEFINE QUESTIONS FROM CURRENT KNOWLEDGE At this point, pupils groups will be set. They will discuss an try to find an aswer to the following questions (if needed, pupils may look then up on the internet), with the guidance of the teacher. What is the nature of sound? How does sound spread? Does it spread differently in different materials? In what way? What are the three main characteristics of sound?

-What does the intensity of the sound depend on? - What does the pitch of the sound depend on? -Could you describe (with the previous scientific terms) what happens in the Doppler effect? (Just describe, we don't intent to explain or proof anything here. The intention is just to transformate the former informal description of the phenomenon into a more scientific one) The answers will be written down and a general discussion will take place until the groups get to some sort of agreement. Teaching Phase 1: Questions Eliciting Activities DEFINE QUESTIONS FROM CURRENT KNOWLEDGE

Teaching Phase 2: Active Investigation PROPOSE PRELIMINARY EXPLANATIONS OR HYPOTHESES -Students propose some possible explanations to the questions that emerged from the previous activity. The teacher identifies possible misconceptions. Based on the previous questions (teaching phase 1) pupils should formulate hypotheses. They should ask the teacher for suitable webs to visit and take information from. Each group should write down its own hypotheses, and then discuss it with the other groups, with the guidance of the teacher.

Teaching Phase 2: Active Investigation PROPOSE PRELIMINARY EXPLANATIONS OR HYPOTHESES Pupils will be introduced to the use of the material provided by Science Center to Go and they will try to argue about how and why the material can modelize the phenomenon. It is important that they focus on the concept of frequency A video depicting the way the material works can be found at:

Use of Science To Go materials, and recopilation of data from the experiments. Each group should fill up a grid with the following data: -Sent frequency -Received frequency (no attention to the equation so far) -Description of the particular situations in which they collected the data (truck moving towards the microphone, away from the microphone) All this is useful to confirm the hipotheses, so they should try to explain wether the evidence gathered from observation fits the hipotheses formulated and what corrections they should make to them. Teaching Phase 3: PLAN AND CONTACT SIMPLE INVESTIGATION and GATHER EVIDENCE FROM OBSERVATION

These hypotheses will be refined along the investigation. The teacher should encourage them to make use of the terms defined before to simplify the work. They can also use the internet to find out more about the phenomenon, if necessary. For example, ml And this two webs with very useful applets: ppler.htm Teaching Phase 3: PLAN AND CONTACT SIMPLE INVESTIGATION and GATHER EVIDENCE FROM OBSERVATION

Here's an example of how one of the applets work

Teaching Phase 4: Discussion EXPLANATION BASED ON EVIDENCE At this point, with all the material the pupils have collected, they should write an essay explaining all the aspects of the phenomenon they can understand. The best way is to create a presentation in a way given in the next slide. There are two very nice videos to show them after they have concluded their investigations, which can help them understand the phenomenon better. The first is more informal, and the second is more rigorous.

Teaching Phase 5: Reflection COMMUNICATE EXPLANATION In turns, each group should communicate to the class the results of the whole investigation, using the presentations they have created. This way the pupils get used to express ideas in a scientific way. The slides should show: -Images explaining the phenomena studied -Grids containing the data collected -Explanations of the phenomena writen in scientific terms -Reflections. Further research needed for explaning the phenomenon in a better way -Conclusions

FOLLOW UP ACTIVITIES AND MATERIALS Advanced learners could try to derive formulas for the Doppler Effect using this web or others: As a follow up activity for all, they may investigate the nature of the light, and its similarities to sound. By means of analogies, they could try to answer questions like these:

-What do the perception of different colours depend on? -Could you make an analogy between colours and the pitch of the sound? -If there is an analogy, why don't we perceive the Doppler effect (related to light) in a daily basis, as we do with sound? -Would it be possible to notice about it with precise instruments? Then they could investigate about the so-called redshift phenomenon and how it is related to the expansion of the universe. FOLLOW UP ACTIVITIES AND MATERIALS