Easy Science Experiments for Kids: Light and Sound

I know it seems churlish to complain about too many beautiful sunny days, and you may roll your eyes when I say that I was sick of the beach, but when I awoke a couple of weeks ago to a grayly spitting sky, it was with some relief.

I knew immediately that it would be a day of cookie baking and science experiments, and combed the boys’ bookshelves for some ideas. Last year I got our oldest several books in a series entitled “Super Science Experiments,” by Miles Kelly, and I pulled out one focused on “Light and Sound Experiments.”

Now while I’m not too lazy to find cool experiments to do with the kids, I am too lazy to allow those experiments to be all complicated and involve tube-line-flange-connectors and tesla-wires and currents and Bunsen burners and safety goggles and such. At 5 and 9 years of age, my kids are too young to delve too deeply anyway, and, more importantly, are disinclined to spend a lot of time setting up anything too intricate or involved.

So, our first experiment required nothing more than

  • a shallow plastic tub
  • some white card paper
  • water
  • a small mirror
  • some sticky tack or modeling clay
  • a flashlight (aka ‘torch’ to those of you inclined to British English)

What you’ll need

You’ll also need a room that you can make pretty dark.

  1. Rest the mirror inside the plastic container, resting on the edge and angled at about 45 degrees. Take a small piece of the sticky tack, and secure the mirror in place.
  2. Fill the container about half way with water.
  3. Stand the white card up at the end of the container opposite the mirror (a thick book or two might help it stay up).
  4. Make the room as dark as possible.
  5. Hold the flashlight about 3 – 4 inches (10 cm) away from the mirror and shine the light through the water and onto the portion of the mirror that is submerged.
  6. Mess around with the angle of the light until you get a rainbow projected onto the white card.

So what does this show? The white light coming from the flashlight is bent as it enters the water, and again as it bounces off the mirror and onto the card. The different colors bend by slightly varying degrees, so the white light splits and you can see each individual color. Yes, you’ve just created a kind of prism that allows you to see the colors of the spectrum.

I’m not gonna lie to you, our version of this experiment was not a tremendous success. The colors were elusive and very faint. But – the kids loved making ripples in the water and watching the reflections bounce around on the ceiling, so they had fun with it anyway. Besides, “Sometimes stuff doesn’t work” is an important lesson in itself for kids.

If you want some follow-up info on rainbows, check out  the Science Kids website.

Our next project showed how filters block out colors. You’ll need:

  • 3 clear glass jars or glasses
  • food coloring
  • water

Yup, that’s it. Fill the jars about 2/3 full with water. Add several drops of food coloring to the jars – red in one, blue in another, and green in the last. (If you don’t have green, this is a great time to show kids how blue and yellow combine to form green.)

Put the glasses in a triangle in a sunny window, with the green glass at the apex of the triangle with the other two behind it. Observe the jars from slightly above them. What do you see?

Each jar lets through only one color of light (for example, the green jar lets through only green light, and blocks red and blue.) Try the same thing with the red and blue jars in front. The same thing happens.

Now look at the jars from eye level, so that you’re peering through combined colors. You’ll see that the colors change. Ask your kids what colors they think each combination has made.

We decided to do something with the leftover colored water, and added about 1/4 cup of salt to each jar, stirred until it dissolved, placed a stone in each one, and set them out in a protected place in the sun.

As the water evaporates, salt crystals form on the stone and the glass. the blue jar has even formed a thin layer of salt above the water’s surface, like ice on a winter puddle. (This will take days, even weeks, but is pretty cool.)

You can also, of course, just let them screw around with the food coloring to make different colors.

Our last experiment of the day, before we got busy making snickerdoodle cookies, involved sound. More precisely, how sound is delayed over distance.

You need:

  • balloons
  • a funnel
  • flour
  • a pin

Place the neck of a balloon over the funnel, and add a few spoonsful of flour, shaking it down into the balloon. Remove the balloon and blow it up, being careful not to inhale or you’ll get a mouthful of flour, as I can unfortunately attest. Tie the balloon.

Go outside and have one person hold the balloon and the pin, while the other walks some distance away. The book suggests 100 paces, at least 50 meters but even better at 75. The person with the balloon holds it away from his body, and pops it with the pin. To the observer, the explosion of flour should precede the popping noise by a fraction of a second.

What does this show? Well, light travels faster than sound, (a lot faster – 300,000,000 meters a second as opposed to speed’s lethargic 340 meters a second) so what you see and what you hear will not happen simultaneously.flour balloon bursting

For a good demonstration of this, sit down with your kids and watch this video of lightning, explaining that the flash and the sound occur at the same time, but the sound is slower so it’s delayed.

Science experiments are a cool way to pass a rainy day (and make some cookies while you’re at it, for goodness’ sake), and far better than vegging out in front of the tv. If you’d like more ideas, see Easy Science Experiments for Kids: Acids and Bases, Easy Science Experiments for Kids: Water, and Easy Science Experiments for Kids: Air.

Happy experimenting!


6 thoughts on “Easy Science Experiments for Kids: Light and Sound

  1. Pingback: Years 5 & 6 Are Smitten with Science | richmond international school

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