To do this activity, I made it very open-ended and exploratory. Students got into groups of 2-3 and i put out various supplies for them to use. I provided cups made of various materials and sizes, string made of various material and of different lengths, and tools to attach the cups and string. I told the students that it was up to them to build a working phone. Many had the right idea of hooking two cups together with the string, but didn't know where to go from there. I let them struggle a little before giving them a few prompts.
1. Describe a sound wave? Main Idea: Sound is created by the vibrations in matter.
2. How could you cause vibrations with your cup and string apparatus?
I let the groups explore after getting these prompts and before long, a few groups figured out that the tightness of the string makes all the difference. I let my class spend the rest of the science on this first day experimenting with different cup setups. They really enjoyed the simple cup phones.
On day 2, we were a little more deliberate. I specified the type of cup and string that would be used for several phones, but students had the option of changing the string length. In another group, I specified the cup and string length, students could change the string material. We did this with several different setups until we found the top 3 phones. From there, we used the scientific method to narrow down which cup material, string material, and string length would create the best phone. Students had to be able to explain why this was the best phone using scientific data from their tests.
I have a formal lab sheet that goes with this activity that I will add to my Teachers Pay Teacher Store: Science Interactions.