Our kids were in their pajamas from Friday night until Sunday noon on what was a cold and rainy weekend. What to do but build a roaring fire in the fireplace, roast chestnuts, bake cookies, and do science experiments?

A while back we had a similar day on which our experiments were themed around air. On Saturday our topic was water, and here’s what we did, all of the experiments sourced from the excellent website The Naked Scientists in their section Kitchen Science.

Our first experiment involved ‘slow waves.’ Take a bottle, fill it 1/3 full with water, and add a drop or two of food coloring. (The kids were fascinated just by seeing the food coloring mix with the water, as you can see from the photo.) Tip the bottle on its side, and gently rock it back and forth, observing the motion of the waves inside. They travel rather quickly.

Now fill the rest of the bottle with vegetable oil, and repeat the wave motion. The waves move much more slowly. Why?

This is a cool demonstration of pressure on the motion of a liquid, and can lead to discussions of water pressure at depth (why objects are crushed at great depth), but mostly they’ll just tip the bottle, shake the bottle, invert the bottle so it looks like a Lava Lamp, etc. Great fun.

Our next experiment involved simple water displacement. Half-fill a glass with water, add a few ice cubes, mark a line at the level of the water, and ask the kids what they think will happen to the level of the water when the ice melts.

Not knowing the properties of displacement, they’ll probably say that the level will go up. (The story goes that when Archimedes discovered this principle, he was lounging in his bath. So excited by the brainwave, he rushed out naked into the streets of Syracuse, Sicily, shouting “Eureka!” – Greek for “I have found it!”)

Now fill a glass with ice until the ice rises above the rim, and pour in water until it is so full that only the surface tension of the water is keeping it from overflowing. The kids will probably guess (correctly) that when the ice melts the water will overflow the glass. But do they know why?

Our third experiment was more exciting for them. Take two bowls, and fill one with cold water, and one with hot water that you’ve just boiled. Cover the hot water and let both bowls rest a few minutes.

Take your food coloring, and tell the kids you’re going to put a drop in each bowl. Ask them if they think the food coloring will react differently in the hot water than it does in the cold. They’ll probably answer ‘yes,’ because why else would you be asking, but press them for how it will behave differently. Dunno. Let’s see.

The drop in the cold water spreads out very little, and drops in a globule to the bottom of the bowl. In the hot water, the food coloring disperses rapidly. Why?

(I’ll give you a hint – both Brownian motion and convection, but you’ll have to read more at The Naked Scientists.)

Our last experiment was probably the easiest, with the most immediate and impressive results. Take a balloon, and rub it on your kid’s hair. Everyone knows what happens next – you’ve created static electricity, and the kids’ hair will stand up when near the balloon. Pretty entertaining in itself, really.

Now turn on the kitchen tap so that a very thin stream of water runs out. Have the kids place the balloon near, but not touching, the stream. It will bend. And the kids will freak out and think that’s super cool. You can briefly and simply explain static electricity and show them this from the Naked Scientist’s page: 

But again, they’ll probably just want to have fun bending the stream, so let them have at it.

There are thousands of interesting experiments you can do with simple items you have on hand around the house. In addition to The Naked Scientists, try Science Kids, which also has fun topics and activities. Well, I’m dying to dissolve the shell of a raw egg in some vinegar, so I guess our next theme will be bases and acids. Can’t wait. Have fun with science!