INSPIRATION
Part of the physics 11 curriculum requires students to “evaluate the validity and limitations of a model or analogy to the phenomenon modelled.” The Doppler effect is an easily modelled phenomenon that applies to many different types of waves and has many applications. Why does a race car’s pitch change as it drives past? Does the Doppler effect happen with water waves or light waves, too? Does the Doppler effect change the volume of a sound?
OBJECTIVE
Students will explore the Doppler effect and characteristics of sound waves by building and assessing the validity of a model: a tiny buzzer and battery assembly that swings at the end of a string.
TRADES CONNECTION
An ultrasound machine allows healthcare specialists a non- invasive way to see inside your body. An image is created by sending very high frequency sound waves into your body and then interpreting the reflected sound waves that bounce back to the machine. Ultrasound machines use the Doppler effect to determine how quickly your blood is flowing: the difference in frequency between the projected sound and the returning sound that is bouncing off moving blood cells allows the machine to quantify the speed of blood movement.
RESOURCE DOWNLOADS
Electrifying Math: Introduction and Glossary
Scientific Method Resource
Part of the physics 11 curriculum requires students to “evaluate the validity and limitations of a model or analogy to the phenomenon modelled.” The Doppler effect is an easily modelled phenomenon that applies to many different types of waves and has many applications. Why does a race car’s pitch change as it drives past? Does the Doppler effect happen with water waves or light waves, too? Does the Doppler effect change the volume of a sound?
OBJECTIVE
Students will explore the Doppler effect and characteristics of sound waves by building and assessing the validity of a model: a tiny buzzer and battery assembly that swings at the end of a string.
TRADES CONNECTION
An ultrasound machine allows healthcare specialists a non- invasive way to see inside your body. An image is created by sending very high frequency sound waves into your body and then interpreting the reflected sound waves that bounce back to the machine. Ultrasound machines use the Doppler effect to determine how quickly your blood is flowing: the difference in frequency between the projected sound and the returning sound that is bouncing off moving blood cells allows the machine to quantify the speed of blood movement.
RESOURCE DOWNLOADS
Electrifying Math: Introduction and Glossary
Scientific Method Resource
Tools & Materials
Material List
- Active buzzer (5V)
- 2-coin batteries (3V 2032 lithium)
- Coin battery holder with switch and lead wires attached
- 1 meter of strong string or yarn
- Cardboard to make a box, or a found matchbox or small container
Tool list
- Scissors
- Electrical tape
- Clear tape
- Sound analyzing software or app that shows sound intensity (Db) vs frequency (Hz) with the ability to zoom in on the graph, such as “Spectrum Analyzer"
- Video and sound recording device (i.e., a smart phone will suffice)
- solder iron and solder
Optional:
Procedure
-
Insert the batteries into the battery holder. -
Turn the switch ON and touch the leads to the buzzer terminals. If no sound is emitted, reverse the leads.
-
Turn the switch OFF and secure the leads to the buzzer terminals. Hook a loop of bare wire of one lead over the buzzer terminal, and twist it onto itself like a twist tie. Repeat for the other battery lead and buzzer terminal. Secure in place with electrical tape (or solder the connection). -
Close the buzzer and battery holder inside the small container, or make a little cardboard and tape box for it. Make sure to leave the switch exposed. -
Secure your string to your buzzer assembly. -
Check your surroundings before using to ensure you don’t hit anything with your Doppler demonstration tool. Find a buddy and take turns swinging it in circles towards and away from each other, about 10' or 3m apart. What does it sound like as it swings toward you? Away from you? What do you already know about sound waves that could help you explain this?
-
Open the sound analyzing app on your phone or tablet. When recording, make sure to swing the buzzer towards and away from the microphone, not just in circles beside or around it. -
Turn the buzzer on and look at the app. Choose the tallest peak on the graph and zoom in on it so it is centred in your screen. Swing your Doppler Demonstration tool in circles towards and away from the phone for about 5 seconds.
-
Take a screen shot of your graph - you should see the current noise peak in green, as well as a wider peak on either side represented by the maximum and minimum readings in red.
-
Look more closely at the graph representation of the noise your buzzer made. What does the y axis represent? What does the x axis represent? What was the lowest frequency the tip of the peak recorded? The highest frequency? The peak when the buzzer was at rest? Think of a few different reasons to explain why the app may have recorded different frequencies while the buzzer was moving vs when it was still.
-
Get nerdy with it! If you measure your string length and you know how many times you swing your buzzer per second, can you calculate how fast the buzzer was moving toward and away from the phone? Can you study the graph on the app, look at the difference in frequency between the maximum, minimum, and stationary sound peaks, and use that information to calculate the speed at which the buzzer was moving? (What other information would you need to solve that?) How different are your two calculated speeds? What might explain any differences you found?
Testing and experimenting
Analyze your data
Extension Challenges
- Wire your buzzer into a circuit for another purpose, such as a high-water alarm, a “fridge door open” alarm, a “cap flap open” buzz indicator to hear if your pet is coming or going, etc... How will you design a switch to complete the circuit to indicate what is happening?
- Make an instructional video for the use of the buzzer as a demonstration tool. Video a swinging buzzer from several different reference points (from the person swinging the buzzer, from above, from a distance in front of the person, etc.) Explain what is causing the pitch changes in each scenario. Upload your video and share it online as an educational resource.
- Make a class set of 25 buzzer demonstration tools (including instructions) and donate them to a local middle school as classroom tools for teachers.