Learn all about sound waves, echolocation, and more. Plus, do a simple project using materials you have at home that demonstrates how sound travels through water and air.
By filling the glasses with different levels of water, you were able to hear how sound travels through a container of water. The sound from the glass with the most water sounded quite a bit different from the one with the least water, and the glasses in between should have created sounds that were gradually higher or lower than the sounds from the first and last glasses. Sound waves can travel through water and when the amount of water in a container changes, the sound you hear changes as well. Do you know why? When you tapped each glass, the sound you heard started out as a vibration of the glass and was quickly transferred to vibrating through the water inside the glass as well. The glass with more water had more matter for the sound to travel through, causing the vibrations to become larger and produce a sound with a lower pitch. To compare, think about a stringed instrument such as a bass or guitar: the thicker strings have more mass and create a lower sound than the thinner strings! The glass with the least amount of water had shorter vibrations and created a sound with a higher pitch.
To take this a step further, you can fine-tune the amount of water in each glass to get even steps in sounds made by each one until you can play a simple song (try "Twinkle-Twinkle Little Star" or "Mary Had a Little Lamb") by tapping on different glasses to play the tune.
Learn all about sound with this science lesson for elementary students.