The Method Draw a wavy line an inch from the bottom of each towel strip, using a different color pen on each. (Older kids should note which color is on which strip.) Dip each strip into the water so that the bottom edge of the paper towel is submerged, but not the line of ink; hold in place as the water creeps up the towel. The ink marks will spread, revealing the different dyes that make up each color.
Most colors are actually made up of several different dyes. As the paper towel draws the liquid out of the bowl, the water molecules bond with the different ink molecules and spread them. The process of separating these dyes (or the components of any mixture) is known as chromatography. You'll likely find that purple leaves a line of blue and a smear of red, and that green breaks up into blue and yellow. As for the black marker, don't be surprised if it's made of different blues -- and even red. To take the exploration further, have your kid cover her eyes while you draw a line on a fresh strip. Dip it into the water; once the ink has spread, have her open her eyes and try to guess which marker you used.
The Method Glue the bottom of the sport-top over the hole in the CD; let dry. Seal the bottle top's base with duct tape, covering the glued area so air can't escape. Stretch the balloon over the spout. With the sport-top open, inflate the balloon by blowing into it through the hole in the CD. Then click the top shut so the balloon stays inflated. Set your creation on a table and gently pull the sport-top open. The air coming out of the balloon will lift your craft; give it a push to send it zipping across the room. Next try pushing the hovercraft while it's deflated. Notice that it moves more slowly.
The inflated balloon wants to shrink back to its natural shape; since it isn't sealed, it pushes air out of the hole in the CD. The force of air escaping lifts the CD, so it hovers above the table, says David Epley, aka Doktor Kaboom!, star and creator of the science DVD Try This at Home. It's a simple lesson about friction. Why does the craft move faster when the balloon is inflated? "Putting the air between the CD and the table keeps them from rubbing against each other, which slows things down."
The Method Glue the base of the plastic cup to one end of the ruler. Once it's dry, create a mini teeter-totter by leaning the center of the ruler against the rock, so the cup faces up. Put a ball in the cup and, with your child standing off to the side of the tiny seesaw, have him press on the other end of the ruler. "This will cause the other end to flip up, and the ball to fly out," says Sean Connolly, author of The Book of Potentially Catastrophic Science. If you press harder, the ball should fly out faster.
For any action, there's an equal and opposite reaction. It's a basic lesson in physics. When you put your force on one end of the ruler, the energy travels to the other end, shooting the ball out of the cup, since there's nothing to stop it. "The teeter-totter creates a lever, a rigid object that pivots on a stationary point (called a fulcrum) and turns a downward force on one end into an upward force at the other end," Connolly explains. "The lever is what actually sends the ball flying." Try making a larger outdoor version of the lever with a board and two buckets (one to stand in for the rock). Test it using a tennis ball and/or a basketball.
The Method Place ice and salt in the large bag. In the small bag, mix the other ingredients. Squeeze out air; seal. Place the small bag inside the big bag. Seal; shake and knead the bag for ten minutes, until the cream thickens. Remove the small bag, rinse, then open and eat the results.
Liquid becomes more solid when its temperature drops. Why? Its molecules slow down and stick together. If they get cold enough and slow enough, they freeze. Here, the ice is colder than the cream and sugar, so it lowers the temperature of the mixture. Adding salt to the ice lowers the temperature even more, so it freezes into ice cream. Why does salt make ice colder? While you're holding the bags, the ice absorbs heat energy from the cream and your hands, so it melts. "Then the water molecules use the energy to freeze again. The salt gets in the way, making them work harder, absorbing and using energy faster," Epley says. This causes the ice and salt to grow colder than plain ice, which helps the cream freeze.
The Method Fill the bag halfway with water; seal it. Hold it at arm's length and help your child poke a sharp pencil through the bag (below the waterline) and out the other side without removing it. The bag won't leak. With the pencil in place, add another. Still, you'll see no drips!
Water molecules need empty airspace in order to flow. Though you're creating holes with the pencil, as long as it's in place it plugs the hole so water can't escape. Of course, you can't plug just anything with a pencil. This experiment highlights some of the properties of common plastics. "It works because the plastic is formed of polymers, molecules strung in long repeating chains," Connolly explains. "The chains stretch to allow the pencil through, then tighten around it, as a turtleneck tightens once it's over your head." Still, if you pull the pencils out, the holes will remain; do it over a sink and see what happens.
Your mini Mozart can conduct his own concert with an orchestra of glasses. Fill eight of them with ascending levels of water to create a scale; create a rainbow effect by adding food coloring. Then have him lightly tap each with a spoon to discover that the different levels create different tones.