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Music is usually considered to be one of the arts, but scientists are interested in sound and music too.

Take a few minutes to sit quietly and just listen. What do you hear? I hear the hum of the computer and the keys clacking as I type this. Do you hear your computer? Beside me I hear a cat purring, behind me the mice are rustling in their cage as they eat their morning snacks. Every once in awhile the parent birds in the shrub outside the window bring food back to their babies and the babies make a terrific racket. Further away I can hear doves cooing and once in awhile, a car passing. These sounds were all around me, but until I sat still and listened, I didn't really hear them. Why do you think that is true? What is sound anyway?

Let's investigate sound by creating some musical instruments. First gather a few materials. A clean, empty tin can with ridges makes a great start. Ask an adult to help you find one, perhaps from the recycling bin. Make sure it doesn't have sharp edges. Now find pencils or chopsticks, rubber bands, balloons, small plastic combs, and some clean, empty bottles with narrow necks.

Think about how you can make sounds using these items. The best musical instruments are the ones you design yourself, but here are a few ideas to get you started. Tap the can with the pencil. How does it sound? Now try rubbing the pencil across the ridges of the can. Try rubbing fast and then slow. You have made a simple guiro, a ridged instrument used in Central America. Do you have anything else with ridges to try?

You can also put a large balloon over the open edge of the can and fasten it down with a rubber band. This creates a cool drum. Or simply blow up a balloon and then hold the opening flat as you let the air out. Can you make a squealing noise? Blow up the balloon, tie it and drum on it.

Can you string the rubber bands across anything to make a guitar? Tie some rubber bands tightly and make others loose. Do they sound different?

What can you do with the bottle? How about blowing over the opening? Hold the opening of the bottle at your bottle lip, and then blow air across the top. This how the musical instrument called the flute produces sound.

Gently touch your various musical instruments while you are playing them. Do you feel anything? You should feel a wavering or vibration. If you are blowing a recorder, can you feel the vibrations on your lips? If you tap on a desk, can you feel the vibrations it makes?

Sound travels as waves, which you feel as vibrations as it passes through the instrument. Here on earth the waves can pass through air because it is made up of gases, and so you can hear someone calling you for dinner. What about in space, where there aren't any gases or substances for the sound waves to pass through? Scientists have predicted, and astronauts have verified, that sound does not pass through empty space.

Oh, I hear the phone ringing, time to go. Now I'm wondering how a telephone works!

Most of you probably recognize this little insect as a praying mantis. But can you tell how small it is? The milkweed flower bud next to it is roughly 1/3 inch long.

The praying mantis is looking for an insect to eat. As it eats and grows, it will shed its exoskeleton or outer "skin." Unlike some insects that change a lot when they grow, the mantis will stay about the same. The biggest change will be that it will have wings when it becomes an adult.

Notice the triangle-shaped head with the large eyes. Those eyes could definitely see me trying to take its picture. It kept hiding behind the flower buds, so I had trouble getting a good photo.

Also notice the front legs tucked up under its body. The praying part of the mantis name comes from that posture. It actually uses those legs to grab prey.

praying mantis nymph

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Thinking of the lovely spring colors, the pastel blues, lavenders, yellows and pinks? Why not try a few really fun experiments creating and changing colors using chemistry?

The first experiment requires some fresh red, blue or purple flowers (purple petunias work really well); a jar big enough to hold a few flowers with a lid; some twist ties, string or yarn to suspend the flowers; household ammonia; and for the optional last part, vinegar (any kind). The ammonia is pretty strong, so this will require help from an adult.

Have an adult pour about 1/2-inch ammonia into the bottom of the jar. Wrap a twist tie or yarn around the stems of the flowers, enough that will fit comfortably into the jar. Suspend the flowers upside-down into the jar so that they are close to, but not touching the ammonia, by wrapping the yarn or twist tie over the lip of the jar. Put the lid on the jar as much as you can. Wait about 15 minutes and you should see the flowers start to change color.

This part of the experiment is based on one by Robert Krampf in his excellent Experiment of the Week series, although I couldn't find it in his archives. Edit: Robert Krampf has revamped his site, and so this link is no longer valid. Check out the fun stuff he has to offer at the Happy Scientist.

Now comes my addition: once the flowers have changed color nicely in the ammonia (which is a base) then try to change the color back by dipping the flowers in a bowl of vinegar (an acid). Using purple petunias, I was able to turn them a bright teal blue in the ammonia, and then back to purple in the vinegar. You can actually dip them into the vinegar, because it won't bleach. It you dip the flowers into the ammonia, however, it may bleach or discolor them. That is why they need to be suspended in the fumes instead.

The second experiment is the classic use of red cabbage as a pH indicator. If you haven't done this, it really is fun. All you need is red cabbage from the grocery store, a blender (ask for an adult's help), glasses or plastic cups and items to mix with the red cabbage solution, such as lemon juice, soda, vinegar, baking soda, dish detergent and laundry detergent.

Some recipes call for boiling the cabbage (smelly!), but I just ground up the fresh red cabbage in small batches with just enough water to allow the blender to work properly. Pour the batches together in a pitcher (which can be placed in the refrigerator for use later in the day if necessary.) Pour about 1/3 cup of the red cabbage juice into testing containers such as clear glasses or plastic cups. Then mix in about a Tablespoon of one of the testing compounds. Does the color change? Try another material in the next glass. Does the color change more if you add more test material? What happens if you mix two materials, like vinegar and laundry detergent? Have fun admiring the wild colors you can make.

What is happening? The pigment molecules in the red cabbage change shape, and thus color, when in the presence of acids versus bases. Lemon juice, vinegar and soda are acids; detergents and soaps are bases.

For the grand finale, create more wild colors with markers. Fold up a diaper wipe that contains alcohol and tie in bunches with rubber bands. Color with Sharpie-type markers. Allow it to set a few minutes and then unfold to reveal a rainbow of colors in a cool tie-dye pattern. Experiment with more wipes to see what you can create. Note: allow to dry suspended on a line so the dye doesn't move onto other surfaces.

If you don't have diaper wipes, then try white fabric. Tie with rubber bands, if desired and then color with markers. Drop or dribble on some rubbing alcohol and the colors should separate and move through the fabric. Once again, keep on a line or suspended until dry. Once you have the technique refined, you might want to create your own tie-dye T-shirts or socks.

Spring colors rock!