How to Make a Phone
One of the most fun experiments for young children, is something that has been enjoyed for many years, likely since "convenience" foods started appearing in cans.
It's the homemade telephone that uses only two soup cans, some strong string, and two paper clips.
To make your phone, open two cans of soup, or a similar size can of goods and don't waste the contents! Wash the cans thoroughly and use a metal file to smooth any rough edges. If you can't quite get the roughness off, cover the can rims with a layer or two of duct tape.
Take a hammer and nail, and put a hole in the center of each can's bottom. Next, cut a length of kite string to use as the conductor, bearing in mind that if it's too short, you'll hear the other person anyway, and if it's too long, you'll lose some conductivity over the distance.
Tie one end of the string through the bend of a paper clip, and thread it through the hole from the inside of one can, until the clip touches the bottom. The other end of the string should be inserted through the hole in the second can's bottom from the outside. Pull it through far enough to tie it to the other paper clip. Stretch out the string gently, until both paper clips are resting against the inside bottoms of the cans.
Now you're ready to "phone" the other person. Stretch the string tightly, and put your mouth right up to the edge of the can. Speak into it, and the vibrations will travel along the string right into the other can.