During this session we examine how sound travels in waves. We experiment with rice vibrating on a drum. We learn how vibration is responsible for the sounds we hear. Vibration can be felt in our throat as we hum. When an object vibrates it makes the air around it vibrate. When the air vibrates fast enough, this movement can be heard as sound. In humans, sound waves enter the ear canal and cause the eardrum to vibrate.
We play a Bat/Moth game and go on a sound nature walk to learn about ultrasound and echolocation. Bats can hear pitches above the human range. Bats emit high-pitched (ultrasonic) sounds through their mouth or nose (depending on species) and listen for the returning echo. Bat sounds are rapid-fire high-pitched calls or clicks. The bats’ ears and brains are so fine-tuned that they can hear the echoes coming back from tiny objects like mosquitoes. They can use the echoes to create a “sound picture” that helps them avoid obstacles while flying and swooping in on their tiny prey. Bats rely on echolocation to capture their food in darkness.
Ultrasound is commonly used to look at how fetuses are doing inside their mother’s wombs. Using an ultrasound machine, millions of high-frequency ultrasonic sound waves are transmitted into the human body—and the reflections, or echoes, they send back are used to see what’s going on inside. Just like a mirror reflects light, an echo is a reflection of sound. When a sound wave rolls through the air and hits a flat surface (such as a wall), some of the energy from the sound wave will be absorbed or transmitted and some of the energy will be reflected so that it bounces back through the air.
DIY Sound Wave Oscilloscope
We experiment with a simple oscilloscope and synthesizer to see sound waves and how they change as a result of changes in pitch and volume.
Bat/Moth game: To play the game, one child is the bat and they are blindfolded. A few children are moths and everyone else is a tree. When bat says “bat” the moths respond by saying “moth”. The bat using sound to catch a moth – this is called echolocation. When a bat gets close to a tree, tree says “tree”. Kids take turn being bat and moths.