The Physics of Waves

1. The Physics of Waves Activity: Moving Sounds 9-12 Science Std: Phys 4a

2. In this activity we will be • Making a device to move sound from one point to another through mechanical transmission • We will look at how sound waves transmit energy and cause things to move • And we will put this idea into practice by: taking sound made in one place changing it into a different type of motion moving it to another place, and changing it back into sound

3. We will be making a Telephone actually, a string telephone

4. OK, so how are we? You will need the following things: 2 plastic cups 2 small sticks 9 feet of string 1 person from each group get these from the side

5. OK, so how are we? You take 2 plastic cups that have holes punched in the bottom…. And you cut a piece of string about 6 feet long… And you put one end of the string through the hole in the bottom of the one cup

6. OK, so how are we? Then you take one of the sticks You tie the string to middle of the stick And put the stick and string in the bottom of the cup

7. OK, so how are we? Then you do the same thing with a cup and a stick on the other end of the string

8. OK, so how are we? Then you take your two cups and move away from each other pulling the string tight Don’t pull too tight or you will pull the string off of the stick But pull tight enough that the string is stretched tight between the two cups

9. So now we are ready to talk Have one person from your group talk into one cup While another person from your group listens at the other cup Make sure you are keeping the string tight while you are talking

10. So now we are ready to talk Then have the person that was listening the first time talk into their cup While the person that talked the first time listens in their cup Does your voice get through the string?

11. Try some other experiments: Will the sound stop if you pinch the string? What happens if you use fishing line instead of the twine for the string? Can you make a string telephone “3-way” call

12. How does this work? When you talked into your cup… Your voice made sound waves that had energy… That hit the bottom of the plastic cup Animation courtesy of Dr. Dan Russell, Kettering University

13. How does this work? The energy from your voice made the bottom of the cup vibrate back and forth – like your eardrum

14. How does this work? The bottom of the cup moving back and forth was sent down the string to the other cup…..

15. How does this work? The string pulled on the bottom of the other cup… making it vibrate back and forth

16. How does this work? The vibration of the bottom of the cup compresses and rarefies the air in the cup making sound waves in the air That you can hear

17. Where else is this used? Where else can sound wave energy move something? How about a microphone? Here’s how it works…

18. Where else is this used? Inside a microphone is a diaphragm that vibrates when sound hits it Just like the bottom of your “cup telephone” This vibration is converted into an electric signal

19. Key Points For This Lesson: Waves carry energy from one place to another Even though waves carry energy through matter, there is no net movement of the matter Sound waves are longitudinal waves Sound waves need a medium to go through – no medium, no sound waves

20. Questions?