Another cool project is called “Hovercraft”! The materials given include: a CD disk, a plastic push/pull bottle cap (“valve”), several balloons, a tube of glue. To compose the system, just glue the cap/valve at the center of the CD. Make sure they are aligned so that the air can flow freely through the hole of CD and the opening of the cap. Wait until the glue dries up (~10 mins).
Push down to close the bottle cap. Now blow up a balloon (use a pump or your mouth:). Quickly place the balloon on the bottle cap and make the connection tight! Hold the cap base and the CD firmly on the floor using one hand and pull to open the valve using the other hand. Let it go! Hooray! Your Hovercraft now floats and moves freely over the floor!
Well, we had fun again! Let us identify the Physics involved in the game.
First of all, when the balloon is blown up, the pressure of the air in the balloon is higher than the atmosphere pressure in the room. As the balloon is connected to the cap and the cap is pulled to open, the air flows through the hole of CD from the balloon to the area between the CD and the floor. Balance of Pressure! The moving air pushes the floor downward and then the floor pushes the air upward. Newton’s Third Law! As a result, the Hovercraft system leaves the floor. As the air continuously flows downward, the Thrust Force balances with the Gravity on the system. The Hovercraft is in a Dynamic Equilibrium: floating over the floor and moving if any random variation! Of course, if thinking even deeper, the flowing air from the balloon to the area between the CD and the floor should also obey the Continuity Principle and the Bernoulli’s principle.
