5th Grader takes on a twist to an old experiment about sound

[Mom_Needs_Help]

My son is working on his 5th grade Science Fair project. His topic is: Can sound travel through yarn as successfully as through string? (Yes, he will be using paper cups/tin cans to conduct this experiment. Also, he will be using thick "crocheting yarn".) We are having a difficult time finding any information regarding how the texture of a solid relates to the ability of sound waves to travel through it. I've found articles explaining the difference in the speed of sound through solid, liquid & gas. However, can you please direct me to links that discuss different "types" of solids? For example, if the yarn is a single, smooth string attached to 2 cups; how will it perform compared to a string of yarn that has been "roughed up" or what happens if the yarn is braided?

[theborg]

Hello mom_needs_help,

Thank you for your question. This is an interesting experiment that should test the elasticity of different string material. Its important to note how the string and cups device works. The string itself isn't actually carrying the sound down it to the cup. What happens is that the bottom of cup 1 vibrates back and fourth in synch with the person speaking into it. If a string is attached to the bottom and pulled very tight it too moves moves back and fourth with the same frequency causing the bottom of cup 2 to move back and fourth precisely like cup 1. The bottom of cup 2 acts like a speaker diaphragm compressing the air inside the cup into longitudinal waves that reproduces the sound from cup 1. This is just what an electronic telephone does, but instead it sends the modulated electric signal that causes a speaker to reproduce the sound of the callers voice. That being said, i think you could test string of different elastic properties to see which work best. I would think the less elastic the better.

For references, look up longitudinal waves, elasticity and periodic motion. To get you started, try these:
http://science.howstuffworks.com/question410.htm
http://hyperphysics.phy-astr.gsu.edu/hbase/permot2.html