Hands-On Sound/Light Demos

Most recent answer: 10/22/2007

Q:
hi im a uiuc student in math. i started in engineering, however, so i have taken phys 111 and 112. that was a few years ago though... anyway, im tutoring a 10 year old boy all summer in various topics. this week were doing science. i need a few cool hands-on activities i can do with him. he wants to learn about sound and light waves. i didnt see anything on your demos page, but maybe i missed it. anything you could send me would be great! thanks! jenna gorman
- jenna gorman (age 22)
uiuc, champaign, il
A:
enna -

Sound and light waves are tough concepts to demonstrate hands-on, but I’ll give it a shot anyways. Let me take them one at a time, though.

When we talk about sound in our shows, we try to have the kids understand that sounds waves are basically what you get when the air jiggles around. Your vocal cords vibrate, making the air next to them vibrate. Then each little bit of air makes the little bits of air next to them vibrate, and so on. We have the kids hold one hand up to their throat and hum in order to imagine this. When they hum, they can feel their throat vibrating from the sound waves.

In order to imagine how each little bit of air moves the next one in waves, you can use a slinky. Stretch the slinky out on the floor. If you give one end of the slinky a little shove (don’t wave it back and forth, just push on one end a bit), you can see a pulse-like wave travel through the slinky. This is much like the way that a sound wave travels through the air.

The pulses come much closer together for high-pitched noises, and much farther apart for low-pitched noises. This is sort of like how a little dog makes a high-pitched bark, since its vocal cords are small and therefore vibrate faster, but a big dog makes a much lower-pitched bark, since its vocal cords are big and therefore vibrate more slowly.

Light, on the other hand, works differently. Light waves actually do move in waves like you normally think of them, moving side to side. You can use the slinky to show this, too. (This is a good way of talking about how light and sound waves are different. Light waves are "transverse" waves, while sound waves are "longitudinal" waves.)

When we talk about light waves at our shows, we like to talk about the difference between different colors of light. A great way to see this is by shining a flashlight through a prism. (This is, of course, more difficult if you don’t have a prism lying around, but you can find them at most toy stores or teaching supply stores, and they’re pretty cheap.) The prism bends the different colors of light different amounts, so you get a rainbow. This also shows that white light is actually made up of all the different colors of the rainbow.

You can find a number of other pictures and topics on light and sound if you check out that section of our answer list. Good luck!

-Tamara

(published on 10/22/2007)

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