Air pressure is one of those things that's strange because we can't see it, yet it is really powerful (holds up airplanes, blows down trees, etc.) When I was learning to fly airplanes, I had a flight instructor (a kind, yet adventurous, soul named Roger taught me to fly) who gave me an analogy for it that is better than any other I've heard.
Basically, he said "Aurora, think of air as being like water. If you have a garden hose and put your thumb over the end, the pressure increases and water sprays out. Same thing with air. Except the increased pressure is under a plane's wings and keeps it up."
Today's experiment shows how squishing air in this way can keep a hovercraft floating on a cushion of air. So, get your glue gun out!
Experiment & Video
What's Going On?
Hovercraft transport people and their stuff across ice, grass, swamp, water, and land. Also known as the Air Cushioned Vehicle (ACV), these machines use air to greatly reduce the sliding friction between the bottom of the vehicle (the skirt) and the ground. This is a great example of how lubrication works – most people think of oil as the only way to reduce sliding friction, but gases work well if done right.
In this case, the readily-available air is shoved downward by the pressure inside of balloon. This air flows down through the nozzle and out the bottom, under the CD, lifting it slightly as it goes and creating a thin layer for the CD to float on.
Although this particular hovercraft only has a 'hovering' option, I'm sure you can quickly figure out how to add a 'thruster' to make it zoom down the table! (Hint - you will need to add a second balloon!)
The stretchy balloon has a higher pressure inside than the surrounding air, and the air is allowed to escape out the nozzle which is attached to the water bottle cap through tiny holes (so the whole balloon doesn't empty out all at once and flip over your hovercraft!) The steady stream of air flows under the CD and creates a cushion of air, raising the whole hovercraft up slightly... which makes the hovercraft easy to slide across a flat table.
I look forward to sharing more fun, excitement and learning with you in our next issue!
P.S. If you'd like to experience one of my free educational (and FUN) online science classes, so you can see first hand how your kids can enjoy learning science... then simply register for my next class by clicking the link below...