Contextualization

Discovered and explained by the Austrian physicist Christian Doppler, the Doppler effect is a phenomenon that occurs when an observer is moving in relation to a wave source. This effect is easily noticed when an ambulance with its siren on passes near us. When the ambulance approaches, the sound seems higher-pitched, and when it moves away, the sound seems lower-pitched. This happens because the speed of sound waves is constant, so when the source moves in relation to the observer, the frequency of the waves perceived by the observer changes. This is the basis of the Doppler Effect.

The most notable application of the Doppler effect in science is in astronomy. "Redshift" or "blueshift" is a phenomenon that occurs when the light from an object that is moving away from us is shifted towards the red end of the light spectrum. This is a direct application of the Doppler Effect and was one of the main pieces of evidence for the Big Bang theory. In addition, the Doppler effect is also used in radar, sonar, speedometers, medicine, and other areas.

We suggest the following references for study:

1. Khan Academy - Doppler Effect: Here you will find explanatory videos and exercises on the topic
2. Brasil Escola - Doppler Effect: Texts and exercises on the Doppler Effect.
3. YouTube - Canal Ciência Todo Dia, Why does the siren change its sound?: Explanation of the Doppler effect through an everyday example.

The objective of this project is to understand and demonstrate the Doppler Effect in practice. To this end, some experimental activities will be carried out. The results of these activities will be used to calculate the apparent frequency and velocity of bodies emitting sound or light.

Practical Activity: Simulating the Doppler Effect

Objective of the Project

The objective of this activity is for students to be able to contextualize, understand and demonstrate the Doppler Effect and its applications through experiments, calculations and analysis. In addition, students will work in teams to plan, execute, and analyze the results obtained.

Description of the Project

In this project, students will simulate the Doppler Effect using a moving sound source and a fixed observer, and vice versa. Furthermore, they will conduct analysis and calculations based on the results obtained, and study applications of the Doppler Effect in areas such as astronomy and medicine, thus integrating knowledge of physics and biology.

Materials Required

1. Smartphone with a sound generator app (can be downloaded for free from the Play Store or App Store).
2. Computer with software for sound frequency analysis (there are several free options available online).
3. Tape measure or measuring tape.
4. Notebook or paper for recording data and calculations.

Step by Step

1. Form groups of 3 to 5 students. This project should be carried out in groups to foster teamwork.

2. With the sound generator app, set it to emit a sound of constant frequency.

3. Move the smartphone in a straight line towards the computer (representing the observer), at a constant, approximate and measured speed.

4. Capture the emitted sound with the sound frequency analysis software on the computer.

5. Do the same experiment, but this time with the computer moving towards the stationary smartphone.

6. Repeat the same process, but this time with the smartphone and computer moving away from each other.

7. Note the observed frequencies in each case and use the Doppler effect equation to calculate the velocities and compare with the actual velocities.

8. Research applications of the Doppler effect in Astronomy (redshift and blueshift) and in medicine (Doppler ultrasound).

Project Delivery and Document Writing

The work carried out in the practice should be reported in the form of a report containing the following topics:

1. Introduction: include a brief explanation of the Doppler effect, its importance and practical applications.
2. Development: explain the theory behind the Doppler Effect, explain in detail how the experiments were carried out, the methodology used and the results obtained. Here, it is also important to discuss the applications of the Doppler Effect in Astronomy and Medicine.
3. Conclusions: summarize the main points of the work, the lessons learned and the conclusions drawn about the project.
4. Bibliography: indicate the sources consulted for the project (books, websites, videos, etc.).

This report must be submitted together with the demonstration of the practical activity. Students should also be prepared to present their project to the class, explaining the objectives, methodology, results obtained and conclusions.