Students consider how our ears work and how a cup phone transmits sound.
Show the slide of the animated transmission from vocal cord to ear. Ask:
Have you ever wondered how my buzzing vocal cords make sounds that can be heard by your ear drum?
How about if you put something in-between, like a cup phone?
Pull out the cup phone(s) and allow students to try it with a partner. They likely have seen cup phones before but may have wondered if they actually work.
(Optional extension: Have available different kinds of cups and lines in different combinations of cup phones. See Teacher Tips for ideas.)
Discuss what makes the cup phone work. Paraphrase:
Our vocal cords vibrate the air inside the cup. The walls of the cup vibrate, making the string vibrate. The vibrations travel down the string to the other cup, which picks up the vibration. The air inside the cup vibrates, and the ear drum picks up these vibrations in the air.
Open the drag-and-drop activity showing How Sound Travels through a Cup Phone.
Let's retrace our steps. How do we get from vocal cords to ear drum?
But this isn't how our real phones work, is it? How is sound transformed into signals that get sent from point to point from one phone to another? Or how do signals travel in different media in any of the other ways that telecommunication devices work?
Today we are going to trace the path of signals going from your mouth to your friend's ear.
Use the blocks to show the order of different media. In the cup example, air is one medium, the paper of the cup is another medium, and the string is another. Each one vibrates to make the next one vibrate, in mechanical waves that move the matter of each medium.
At any point did the sound travel at the speed of light? Did it ever "skip over" needing a medium?