by: Jim Fiddes I recently used this extension of the balloon-CD hovercraft plans in Norm Barstow’s blog for a middle school physical science lab, but it could be easily adapted for a high school IPS class. It works as inquiry for higher-achieving students, but just as well with more detailed direction, for regular classes. By the time you do this collision addition, your students should be attuned to the fact that “hover” means just that—there is no lateral motion without some sort of propelling force. The hovercraft will just sort of sit there and maybe spin a little. Students looking for more dynamic action will be disappointed. As a mid-point review between the two hovercraft labs, you may show the “Junkyard Wars” episode on hovercraft, in which it’s abundantly clear that hovercraft need two forces—one to levitate the craft, and another to propel it. Students provide the propelling force, accelerating one levitating hovercraft into another, and observing the results. Illustration: www.xinventions.com Basically, this addition explores the ideas of Newton’s Three Laws, inertia, momentum (First Law), Newton’s Second Law (force equals mass times acceleration), and even Newton’s Third Law (action-reaction) using collisions between differently-weighted hovercraft. Weighting is done with the simple addition of pennies or washers onto the CD (see below). While it’s difficult to quantify acceleration here, mass can be calculated and compared. If you have a SmartBoard, you can do some cool on-screen demos as lab prep and summary, too! More about this later! Read the rest of this entry »
by: Norm Barstow
The first practical design of the hovercraft was completed in the late 1950’s by British engineer, Sir Christopher Cockerell. Since then, the continued development of this invention has been ongoing, and currently, the hovercraft is being used commercially, by the military, and for personal use. Teachers have been constructing versions of the hovercraft using balloons, film canisters and flat materials in classrooms for years.
The principle behind the hovercraft’s levitation is that when the air is released from the balloon, it hits the ground and rushes outward in all directions. The air flowing from the balloon through the holes forms a layer of air between the hovercraft and the table. This reduces the friction (the resistance that occurs when two object rub against each other) that would have existed if the hovercraft rested directly on the table. With less friction, your hovercraft scoots across the table.
Furthermore, extra air molecules are packed underneath the structure, which in turn increases the pressure under the hovercraft. This increased pressure below the craft produces an overall upward pressure force on the craft therefore it supports its weight. Since air molecules are always leaking out from beneath the craft, you’ll need a source of air molecules to replace them, which is provided by the balloon.
- Large balloon (12”-16”)
- One plastic film canister
- Hovercraft base: choose from one of the following:
· Large plastic plate (not the inflexible type)
· Foam meat tray from grocery store (6.5” X 8.5”)
· Old CD
· Stiff cardboard
- Poster putty such as Blue Tak, or Poster Tak
- Smooth surface
- Hole instrument: Ball point pen tip or hot nail or drill.