January 19 is National Tin Can Day. Yep, there really is a day for everything it seems. So why recognize this one? Well, we can’t pass up the opportunity for some hands-on learning! Tin cans are celebrated for the advancements they brought to food preservation in the early 1800s. Outside of their primary purpose, I’m thinking about celebrating the science of the tin can telephones. The Guinness World Record for the longest functioning tin can telephone is 796 feet!
While tin can telephones are primarily used today to learn about sound and vibration, versions of the tin can telephone were made in the 1700s and sold into the late 1800s. Such designs were used until Alexander Graham Bell’s telephone gained popularity and took over the telephone market as we know it. When you think about how these simple components come together to transmit sounds over a great distance, it’s almost like magic – or at least that’s what I thought when I was a kid. Well, I know behind magic, there is often science.
Making a tin can telephone is an easy and fun project. Follow these steps to get started.
Sound travels as waves through a medium. When a teacher speaks to a classroom, the medium is the air in the classroom. The particles in the air are very spread out, so sound can’t travel very far. The particles in a string are packed more closely together and help the sound waves travel a greater distance.
As you speak, your vocal cords create vibrations that push through the air to the front of your mouth. This air creates vibrations in the form of compression waves. The vibrations travel out of your mouth, into the can, and down the string to the other can. Our ears feel the vibrations and turn them into electric signals for our brain to interpret. The string must remain tight in a straight path for the waves to travel down. Remember, the string is carrying the vibrations from one can to another.
One of the difficult things about understanding sound and sound waves is that you can’t see them. You can, however, use a simple experiment to make them visible. Tightly cover a bowl (or even a tin can 🙂) with plastic wrap. Sprinkle the plastic wrap with salt, rice, or other small objects. Then, it’s time to make some noise. You can snap your fingers, hit a metal object such as a pan, or even play music from a cellphone speaker near the bowl to watch the salt or other objects dance with the vibrations of the sound waves. This is a simple cymatics experiment. Cymatics is the process of making the sound visible by vibrating a medium.
You can also download a variation of this activity – using sprinkles – from our STEM Anywhere page.
And, while you’re trying those out, explore some of these books to keep the excitement going!