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Hovercraft by Rachel and Sara

Who doesn't love to rise above it all? We're into engineering, so we built our own hovercraft. But it didn't work very well on grass. Our question: How can we optimize our design to create the best air film?

What did we do?
A hovercraft works best by creating a cushion of air with enough pressure to support the weight of the craft and a passenger. A fan blows air underneath the hovercraft platform, and air is trapped between the platform and the ground by a piece of material called the skirt. A small amount of air leaks out from under the skirt, creating the cushion of air. To try to improve our hovercraft's performance, we tried two skirt designs: one was loose and baggy, one was tight. We fired up each hovercraft over a pile of glitter to see how the leaking air scattered it around. We put each craft through a speed course and an obstacle course to see how they performed.

What did we find out?
The tight skirt made the air escape quickly out the side, scattering the glitter everywhere. The baggier skirt created a slower leak of air, and barely scattered the glitter. This seemed to be what we wanted, because the tight skirt hovercraft didn't perform as well as the baggy skirt hovercraft in the speed and obstacle courses.

What can you do?
• Use an air hockey table for a science investigation. Find things around the house that might work as hovercrafts on an air hockey table. How does the amount of surface area relate to the amount of weight it can carry and still hover?

• Make your own hot air balloon from a lightweight plastic bag, paper band, thread, cellophane tape, and paper clips. Inflate the bag with hot air from a hair dryer. When it's full, release it, and try to measure how high the balloon flies, and time how long it stays in the air before returning.

• Get a helium-filled balloon and tie a small sand bag to the bottom. Adjust the amount of sand in the bag until the balloon floats just off the ground. How does the size of the balloon compare to the weight of sand in the sand bag?

• Use this hovercraft investigation as a science fair project idea for your elementary or middle school science fair! Then tell us about it!