The Doppler Effect

• databot with sound and distance
  sensor

• IOS/Android Smart Device

Investigations

Physical Science

Background

What You Will Need/Prep

• Test your databot™ connection.

• You will be prompted to select
  and connect to databot™ each
  time you launch an experiment.

• If there are two or more
  databot™'s listed, the one
  closest to your device will be
  highlighted in blue.

The Doppler Effect

Overview

• Install Vizeey™ on your
  Smart device.

• Study the background
  information and terms and
  prepare to explore!

Grades: Middle School

Time: 45 Minutes

Subject: Physical Science

Topics: Doppler effect, Sound, Sound
Waves, Speed of Sound

• Tuning Fork

• Ruler or measuring tape

Learning Objectives

By completing this lab, students will:

• Understand the principles behind the Doppler effect and its relationship to wave
  frequency, wavelength, and relative motion.

• Identify and explain how motion of a sound source or observer affects the perceived
  pitch of sound.

• Observe and measure changes in sound frequency using databot’s sound sensor
  during motion experiments.

• Analyze recorded data to identify patterns in frequency shifts caused by the Doppler
  effect.

• Connect experimental observations to theoretical principles of wave behavior in moving
  systems.

• Visualize and interpret changes in sound wave data using graphs to deepen their
  understanding of how the Doppler effect works.

Doppler Effect: A change in the observed frequency of a wave caused by the relative
motion between the source of the wave and the observer.

Frequency: The number of wave cycles passing a point per second, measured in hertz
(Hz). Determines the pitch of sound.

Pitch: The perceived highness or lowness of a sound, directly related to the frequency of
the sound waves.

Relative Motion: The movement of the wave source, the observer, or both, which affects
the observed frequency due to the Doppler effect.

Sound Sensor: A device used to detect and measure sound waves, often used to observe
changes in frequency and intensity.

Sound Wave: A vibration that travels through a medium (e.g., air) as a longitudinal wave,
compressing and rarefying particles in the medium.

In this activity, you will investigate the Doppler effect and
learn how motion influences the frequency and pitch of
sound. Using a databot’s sound sensor and simple
experiments, you’ll observe and analyze how sound waves
behave when their source or the listener is in motion.

Press this button to start

the experiment.

• Graph showing the sound level

In order to work with the experiment you need to launch the Vizeey application and click on
+ in the upper right corner.

Then select “Add experiment from QR code” and scan the QR code prepared for this
experiment. Your experiment will appear in the list.

When you start the experiment you will be immediately
offered to connect to your databot. Make sure that databot
is turned on and in Vizeey mode with a blue blinking light.

• Sound intensity value in real-time.

This lab work investigates the Doppler effect

The lab work will involve generating a sound
source of different frequencies. To do this, scan
the qr code with your phone.

Set the frequency

Start the sound

• Maximum sound value

• The experiment contains several tabs.

Part 2: Hypothesis

Part 1: Initial Observations and Discussion Questions

If the source and the observer are moving at the same speed in the same direction, will
the Doppler effect still occur? Why or why not?

Part 3: Experiment Procedure

Based on your understanding of sound waves and motion, propose a hypothesis about
how the Doppler effect could be observed and measured using a databot sound sensor.
Consider how changes in frequency might occur when the sound source or observer is in
motion, and how this data could be used to confirm the principles of the Doppler effect.
Predict the relationship between the speed of motion and the observed change in sound
frequency.

The Doppler effect is a change in the frequency
or pitch of a wave. When a source moves
toward the observer, the waves compress,
resulting in an increase in frequency and pitch.
Conversely, when the source moves away, the
waves stretch, decreasing the frequency and
pitch of the tone. This phenomenon is
commonly observed with the sound of a
passing siren. It illustrates the relationship
between motion and wave behavior.

Demonstration of the Doppler effect using available materials and minimal space.

Part 3: Experiment Procedure

The Doppler effect is used in various real-life applications:

• Radar and Speed Measurement: Doppler radar is used by police to measure the speed
  of vehicles by detecting the frequency shift of radio waves reflected from moving cars.

• Medical Imaging: In ultrasound technology, the Doppler effect helps to measure blood
  flow by detecting changes in the frequency of sound waves bouncing off moving blood
  cells.

• Astronomy: Astronomers use the Doppler effect to determine the speed and direction
  of stars, planets, and galaxies by observing shifts in the frequency of light or radio
  waves they emit.

• Weather Forecasting: Doppler radar is also used in meteorology to track storms and
  precipitation, as it detects the movement of rain or snow particles through frequency
  shifts in radio waves.

• Scan the provided QR code with your smartphone to access the sound generator.

• Choose a constant frequency (e.g., 440 Hz, or any other of your choice).

• Securely attach the smartphone to one end of the string. Ensure it is tightly fastened to
  avoid slipping.

• Play the selected tone on the smartphone.

• One student stands in the center of the classroom, holding the other end of the string,
  and begins rotating the smartphone in a circular motion above their head.

• The rest of the students stand at a safe distance, listening carefully as the smartphone
  moves closer to and farther from their position.

• Pay attention to how the sound changes as the phone moves. When the phone
  approaches, the pitch will rise when it moves away, the pitch will drop.

Sound Generator

Ensure the rotating area is clear, and students maintain a safe distance to avoid
accidents.

Effect Observed:

As the phone moves closer to the listeners, the pitch of the sound becomes higher. When it
moves away, the pitch becomes lower.

Why It Happens:

This occurs due to the Doppler effect: the motion of the sound source compresses sound
waves when approaching, increasing their frequency (higher pitch), and stretches them
when receding, decreasing their frequency (lower pitch).

• Place databot on a flat surface, such as a table, in a space where sound can travel
  freely.

• Set up a sound source (any speaker generating a frequency around 7000 Hz, which is
  optimal for the databot's sensor)

• Begin playing the sound at a steady frequency, ensuring the sound is continuous and
  stable.

• Move with the Sound Source: Walk at a constant speed while holding or carrying the
  sound source, passing by the databot

• Open the Vizeey app on your smart device.

• Turn on databot (using the small button on the left side)

• Tap on "The Doppler Effect" in Vizeey to load the experiment.

• You will be prompted to connect to databot.

  • Hint- if there is more than one databot in use, the one closest to you will be in blue!

  • A solid blue light on databot means you are connected.

• Start your experiment using:

  • Use these icons at the top of the screen in Vizeey to start and to pause the
    experiment.

Observe the Graph: Watch the graph on the
databot’s screen as you move. You’ll notice
that as you approach the databot, the
frequency detected by the sensor increases,
and the distance between the peaks on the
graph becomes smaller. Conversely, when
moving away from the databot, the frequency
detected decreases, and the distance
between the peaks becomes larger.

When you approached databot

When you moved away from databot

If you don't succeed the first time, repeat this experiment.

Effect of Distance on Sound

Sound intensity and the Doppler effect are related indirectly

The intensity of sound decreases as the distance between the sound source and the
observer increases. This happens because sound energy spreads over a larger area as it
travels, and less energy reaches a specific point the farther it moves.

The intensity of sound is inversely proportional to the square of the distance from the
source. This is known as the inverse square law. For example, doubling the distance
reduces the sound intensity to one-fourth.

Tuning Fork

databot 3

databot 2

databot 1

Fill in the table indicating the distance from the tuning fork to the databot as well as the
maximum sound value

Make a histogram of the resulting values

In the Vizeey app, navigate to the “Game” tab to begin the experiment.

• Position the databot as close as possible to the tuning fork to capture the maximum
  sound intensity.

• Initiate the experiment using and striking the tuning fork. A sound wave of a certain
  intensity will be generated, and it will appear on the graph in white.

• Gradually move the databot away from the tuning fork. As you do, the graph of the
  sound intensity will change, showing a decrease in intensity as the distance increases.

• At the same time, the distance sensor graph will show the change in distance as you
  move the databot.

• The Challenge: Your task is to adjust the movement of databot so that the sound
  intensity graph and the distance graph align as closely as possible. Try to make them
  match!

Part 3: Experiment Procedure

Now, let's turn this into a fun game of skill and understanding!

Did you manage to realize it?

1. What additional experiments or observations could you make to further explore the
   Doppler effect?

Part 6: Reflection

2. How would you modify this experiment to study the Doppler effect with light waves
instead of sound?

3. How would the results of this experiment change if the sound source were moving in a
circular path instead of in a straight line?

4. Could the Doppler effect be observed with objects moving at constant speed? How
would the shift compare to objects accelerating or decelerating?