Crafted from cardboard, this nifty vessel runs on the same principles as the hovercrafts that ply the English Channel, and it has a great physics lesson stowed away in its simple design.
First, have your kids push their hovercrafts across a table without blowing up the balloons. They don't move very far because of the friction between the two surfaces. When the balloon is inflated, it creates a cushion of air between the cardboard and the table so the balloon zips along. Have your kids deploy their hovercrafts on a rug, asphalt, and a smooth surface to see which makes the speediest racetrack.
"Kids will come up with their own experiments," says Shari Hartshorn, a Science Museum of Minnesota employee. She's seen hovercraft races, competitions to see how much weight a hovercraft can carry, and even hockey games, complete with goalposts.
Decorate one side of the cardboard square by attaching stickers or magazine pictures with a glue stick. Flip over the square and find its center by drawing two lines between opposite corners, making a big X. Poke the pencil through the center of the X to create a pencil-size hole.
On the decorated side of the cardboard, squirt a ring of hot glue around (but not in) the hole. Carefully place the thread spool in the center of the cardboard, its hole aligned with the pencil hole, and press together.
When the glue has set, blow up the balloon and twist the neck to keep the air in, then stretch the opening over the top of the spool. Set the hovercraft on a smooth, flat surface, untwist the balloon, give it a push, and then watch it go!