Everything on this page is a real experiment with a real explanation. No magic, no "it just does that." Kids can handle the truth about why a balloon inflates, and they remember it better when it makes sense. Each one uses things you probably already have in the kitchen, takes an afternoon or less, and comes with a safety note, because "safe" is the first word in the title for a reason.

What to do:

1. Pour the vinegar into the bottle.
2. Using the funnel, put the baking soda into the balloon. Shake it down into the bottom.
3. Stretch the mouth of the balloon over the mouth of the bottle, carefully, without letting the baking soda fall in yet. The balloon flops over to the side.
4. When you're ready, lift the balloon upright so the baking soda pours into the vinegar. Stand back and watch.

Why: Baking soda is sodium bicarbonate, a base. Vinegar is a weak solution of acetic acid. When an acid and a base meet, they react. This particular reaction produces carbon dioxide gas (plus water and a salt called sodium acetate that stays dissolved). A gas takes up much, much more room than the solid and liquid that made it, so the carbon dioxide has nowhere to go but up into the balloon. The bubbles you see are the gas escaping the liquid. When the fizzing stops, one of the two ingredients has been used up, and the balloon stops growing.

Try this: Do it again with twice the baking soda. Then with twice the vinegar. Which one made the balloon bigger? (There's a correct answer, and your kids can find it by testing, which is exactly what scientists do.)

You need: half a head of red (purple) cabbage, a knife and cutting board, a pot, a strainer, several clear glasses or white cups, and things to test: white vinegar, lemon juice, baking soda dissolved in water, dish soap in water, plain tap water, club soda, milk, and whatever else is in the fridge that's safe to touch.

What to do:

1. Grown-up step: Chop the cabbage into small pieces, put it in the pot, cover it with water, and bring it to a boil. Simmer about 10 minutes, until the water is a deep purple. Turn it off and let it cool.
2. Strain the purple liquid into a pitcher. (Cook the cabbage for dinner; it's fine.) This is your indicator.
3. Pour about a quarter cup of indicator into each glass.
4. Add a spoonful of one test substance to each glass and watch the color change. Line them up and compare.

Why: Red cabbage gets its color from pigments called anthocyanins. The shape of these molecules changes depending on how many hydrogen ions are around them, and the shape determines what color of light they absorb. Acids (vinegar, lemon) have lots of hydrogen ions and push the pigment to its red form. Bases (baking soda, soap) have few, and push it toward blue and green. Chemists measure this on the pH scale: 7 is neutral, below 7 is acid, above 7 is base. Your cabbage juice is a homemade pH meter. The real litmus paper in a lab works the same way, with a pigment from lichen.

Try this: Add vinegar to the blue baking-soda glass a little at a time. Can you get it back to purple? That's neutralizing a base with an acid. (It'll fizz, too. See experiment 1 for why.) Also try soaking coffee filters in the indicator and letting them dry. You've made your own test strips.

You need: 3 cups of white sugar, 1 cup of water, a saucepan, a clean glass jar, a wooden skewer or a piece of clean cotton string, a clothespin or pencil to hang it from, and a paper clip if you're using string.

What to do:

1. Grown-up step: Heat the water in the saucepan until it boils. Add the sugar about half a cup at a time, stirring until each addition dissolves completely before adding the next. When all 3 cups are dissolved and the syrup is clear, take it off the heat. (If you want colored candy, add a few drops of food coloring now.)
2. Let it cool for about 10 minutes, then carefully pour it into the jar.
3. Wet the skewer (or string) and roll it in dry sugar, and let it dry for a few minutes. These sugar grains are "seeds" for the crystals to grow on.
4. Hang the skewer in the jar so it's in the syrup but not touching the bottom or sides. A clothespin laid across the jar mouth works. If you're using string, tie a paper clip to the bottom as a weight.
5. Cover loosely with a paper towel and put it somewhere it won't be bumped. Now wait. Check every day but don't move it.

Why: Hot water can dissolve much more sugar than cold water. At boiling you dissolved 3 cups of sugar in 1 cup of water, far more than would dissolve at room temperature. As the syrup cools it becomes supersaturated: it is holding more sugar than it "wants" to, and that extra sugar has to come out of solution. Sugar molecules leave the liquid and attach to the seed crystals on the skewer, lining up in the same repeating pattern as the crystals already there, so the crystals grow. As water slowly evaporates over the week, even more sugar has to come out, and the crystals keep getting bigger. Look at the finished crystals with a magnifying glass: the flat faces and sharp angles are the shape of sugar molecules stacking up, millions and millions of times.

Try this: Grow a second jar in the fridge and a third in a warm spot. Which grows crystals faster? Which grows bigger ones?

What to do:

1. Pour honey into the glass to about a third full. Pour it in the middle, not down the sides.
2. Color some water with a few drops of food coloring. Pour it slowly down the inside of the glass, or over the back of a spoon, so it lands gently on the honey. Another third.
3. Pour the oil in the same slow way on top.
4. Now you have three layers. Drop in the small objects one at a time, and see where each one stops.

Why: Density is how much stuff is packed into a given amount of space, how heavy something is for its size. Honey is about 1.4 times as dense as water; vegetable oil is a little less dense than water, about 0.9. Each liquid floats on any liquid denser than itself and sinks through any liquid less dense. The objects do the same thing: each one sinks until it reaches a liquid denser than it is, and floats there. A grape is a bit denser than water but less dense than honey, so that's where it stops. This is also why a ship made of steel floats: the ship as a whole, with all the air inside it, is less dense than water even though the steel isn't.

Water and oil also refuse to mix for another reason (water molecules are attracted to each other much more than to oil molecules), which is why you can even shake this and, given time, it will separate into layers again.

Try this: Add a fourth layer. Where would corn syrup go? Dish soap? Rubbing alcohol (carefully, it's less dense than oil)? Predict first, then test. Also try dropping in an egg: it sinks in water but floats in very salty water, because salt makes the water denser.

You need: a glass jar or coffee can with a wide mouth, a balloon, scissors, a strong rubber band, a drinking straw, tape, an index card, and a pencil.

What to do:

1. Cut the neck off the balloon and stretch the rest tightly over the mouth of the jar like a drum head. Hold it on with the rubber band. It should be tight and flat.
2. Tape one end of the straw to the middle of the balloon, lying flat, so most of the straw sticks out past the edge of the jar like a pointer. Cut the free end at an angle so it makes a sharp point.
3. Stand the index card up next to the jar (tape it to a book or the wall) so the straw tip points at it. Mark where the tip is right now and write today's date.
4. Put the whole thing somewhere the temperature stays about the same, out of the sun and away from heaters and windows. Check it once or twice a day and mark the card. Also write down what the weather is doing.

Why: You've sealed a pocket of air inside the jar at whatever the pressure was when you stretched the balloon on. The air outside is always changing pressure as weather systems move through. When the outside pressure goes up (high pressure, usually fair weather), it pushes down on the balloon and dents it in slightly; the straw, like a see-saw, tips so the pointer goes up. When the outside pressure goes down (a low, usually clouds and storms), the air trapped in the jar pushes the balloon up into a slight dome, and the pointer goes down. The movement is small but you can see it, and the straw makes it bigger by acting as a lever.

One honest caveat: the air in the jar also expands when it gets warm and shrinks when it gets cold, and that moves the pointer too. That's why it has to sit somewhere with a steady temperature. A real barometer uses a sealed metal chamber with the air pumped out, so temperature doesn't matter as much. Ours is a bit crude but it's the same principle.

Try this: Keep a chart for a month with the pointer position and the weather each day. Do the drops come before the rain? Compare your readings with the pressure they announce on the TV weather. Then go read what a real cooperative weather observer does at Weather Watching with Walter, a page I found on GeoCities.us that I keep going back to.

What to do:

1. Blow up the balloon and tie it.
2. Rub it briskly on your hair (or the sweater) about twenty times, always in the same direction.
3. Stunt 1: Hold the balloon a few inches above the confetti. The bits jump up and stick to it.
4. Stunt 2: Hold it near your hair without touching. Your hair stands up and reaches for it.
5. Stunt 3: Press it against a wall and let go. It stays there.
6. Stunt 4 (the best one): Turn on the faucet to a thin, smooth stream, as thin as you can get it without breaking into drops. Rub the balloon again and bring it slowly toward the stream, without touching. The stream of water bends toward the balloon.

The wall and the paper aren't charged to begin with, so why do they stick? Because the negative balloon pushes the electrons in the wall's surface a tiny bit away from it, leaving the nearest part of the wall slightly positive. That's enough to hold a balloon. The water stream bends for a related reason: water molecules have a slightly positive end and a slightly negative end, and near the balloon they swing around to point their positive ends at it and get pulled toward it.

This is the same electricity as the shock from a doorknob in winter and the crackle when you pull off a sweater in the dark, just on a very small and very safe scale. Lightning is the same idea on a very large and very unsafe scale.

Try this: Rub two balloons on your hair and hang them from strings side by side. They push apart. Now rub only one. What happens? See if a balloon rubbed on a plastic bag works better or worse than one rubbed on hair. Does it work with a wet balloon? (No, and can you figure out why?)

• Predict first. Before you drop the grape in, ask "where do you think it'll stop?" Being wrong is not a problem. Being wrong and then finding out why is the whole of science.
• Keep a notebook. A composition book with the date, what you did, what happened, and a drawing. My ten-year-old's is a treasure.
• It's okay to say "I don't know." Follow it with "let's find out." The library is full of the answers, and so, increasingly, is the internet, though check who wrote the page.
• When it doesn't work, that's data. The static balloon fails on humid days. That's not a failed experiment; that's a discovery about humidity.
• Let it be messy. Cookie sheet. Old clothes. Paper towels. Then it's not a problem, it's a lab.