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# CD Hovercraft

You can make a hovercraft from the comfort of your home! For this DIY science, all you need are a few things that you probably already have around your house: a CD (preferably one that you never want to listen to again), a bottle cap (preferably resealable, otherwise just poke a hole through the center), a balloon, and glue. Glue the CD to the bottle cap, then let it dry. The more complete a seal you form between the cap and CD, the better your hovercraft will perform; so don’t be afraid to hit any weak spots with some more glue. Cover the bottle cap with the balloon and blow it up. Place it down on a smooth, flat surface like a floor, table, etc. and let it go. It’s as simple as that!

Air from the balloon wants to escape through the hole in the cap, due to air pressure on the outside of the balloon. We usually experience air pressure as the force from the atmosphere pushing down on us. Here at AstroCamp we feel about twelve PSI, or pounds per square inch. The force of the air pushing down and out of the balloon lifts the hovercraft. This is just like Newton’s Third Law of Physics, which states that for every action there is an equal and opposite reaction. In this case, the air pushing down on the table causes a push back on the hovercraft itself, lifting it up.

The hovercraft lifting up allows more air to flow out of the balloon and all around the CD, effectively creating a new surface for the hovercraft to rest on, which is air! It turns out that something doesn’t have to be a solid to be a surface. The new air surface is nearly frictionless which allows our hovercraft to seemingly glide across!

The hovercraft works very similarly to how an air hockey table works, though the directions of air flow and force are reversed. An air hockey table has a ton of tiny little holes all over it that shoot air upwards. That air lifts the puck and lets it glide across the table like a little hovercraft. It’s really just gliding along on the tiny jets of air!