Using the Kick-Disc Hovercraft toTeach Introductory PhysicsConcepts in Kinematics andDynamicsBy: Nils Sorensen Course: PH690Professor: Dr. MacIsaacUsing a Kick-Disc to Teach Introductory PhysicsAbstract: The Kick Disc is a smallrechargeable hovercraft that providesadvantages for teaching introductory physicsstudents the ideas of kinematics anddynamics. This paper will introduce a fewactivities for teachers that use the Kick Discas the vehicle for discovery. The activitiesdescribed focus mainly on kinematics withsome references to beginning dynamics.Hovercraft History:The idea of Air Cushion Vehicles (Hovercraft) originated with a British engineer, John Isaac Thornycroft, who worked on ways to reducehull friction using air. This led him to hydrofoils rather than what we think of as hovercraft floatingon a cushion of air, but it didhowever depend on placing airbetween water and a boat’shull. During World War I, thecoastal defense boats that hedeveloped were achievingspeeds of up to 45 miles perhour. The first air cushionvehicle was produced by aFinnish engineer, DI Toivo J.Kaario in the 1930’s but itnever received the fundingrequired for development.Real development took place in the 1950’s in England. Christopher Cockerell purchased existing US patents and developed the hovercraft so that in 1959 one of his craft crossed the Channel between France and England. Today, hovercrafts are best known as car-ferries betweenEngland and the Continent but they are more widely used in marine rescue because of their ability to move easily over flat beach as well aswater. The ability of air cushion vehicles to move heavy loads over nasty terrain such as swamps, mud flats, or smooth ice were not appreciated until the 1970’s.Hovercraft in Physics Instruction:Hovercraft in physics instruction may have originated in the 1960’s withPSSC (PhysicalScience StudyCommittee)films that usedQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.machined brass discs (pucks) with what appeared to be a toilet tank float machined into the top surface. The tank was filled with dry ice and tightly corked. The carbon dioxide gas, generated by the warmed dry ice, escaped through a small hole that connected the tank with the bottom of the disc. These discs floated effortlessly over horizontal glass surfaces.In more recent times these PSSC films have been resurrected and achieved some popularity as a part of the program “Physics Cinema Classics”. These films are helpful, but do not put physics into the hands of the students who need direct experience with these materials and situations. The PSSC low friction discs were never developed and sold by science education supply houses for the simple reason that they were too expensive for schools to afford. They had the additional liability of requiring a ready supply of dry ice. It was obvious however that there was an interest in developing low friction devices for physics educationbecause a number of them appeared on the market in the 1970’s. Oneof these was very similar to the PSSC system but the puck was hard plastic and the dry ice container wasreplaced with a balloon. These were veryinexpensive and worked if all you wantedwas something that would glide for about 1meter. These did a somewhat convincingjob of illustrating the 1st Law.Unfortunately, in order to get any “get upand go”, the balloon had to be large incomparison to the puck so the balloon bentbackwards and sideways in the wind,touched the table surface and the puckceased to glide nicely. Recently the plasticpuck has been replaced by a Compact Disc,but that fails to correct its major problem, the balloon.Another attempt used the same plastic pucks rolling on ball bearing like plastic beads. This required a smooth tray; preferably glass, to restrict the beads and puck, something like a pool table restricts pool balls. The beads created a low friction surface for objectsto roll on.Air tracks provided an excellent frictionlesssurface, but required an external air supply that wasso noisy; it prevented the teacher from effectivecommunication during the lesson. The air trackswere also delicate, expensive, and allowed onlylinear motion.Some teachers with extra cash and lots ofspace purchased air hockey tables. These were fun and effective for QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Diameter:18.5 cm/ 7.25 indemonstrations but did not lend themselves to use by large numbers of students. This equipment solution never seemed to catch on.Today’s favorite low friction device seems tobe the Pasco cart. These are effective in onedimension and relatively inexpensive. Theirdisadvantage for introducing kinematics and the1st law is that they are moderately expensive andlook like the serious physics equipment that theyare. This can be off-putting at an introductorylevel.Behold the “Kick Disc”; an air-powereddisc that has been introduced into the physicseducation market in the last two years. Itlooks like a toy and can be used on the floorby teachers doing demonstrations or evenbetter by small groups of students working ontheir own. The discs are relatively cheap ($25)and small enough so they can be easilystored. The rechargeable battery makes iteasy to keep them fully charged so that moreconsistent operation can be maintained overan entire class period. What follows is a guidefor teachers to incorporate the kick-disc intotheir physics classes. The activities provideteachers with ways to help studentsinvestigate kinematics and dynamics, as well as offer suggestions on how to assess the learning that has occurred.Kick Disc Construction:The Kick Disc has a verysimple and straightforwardconstruction. It is a 6-volt motorwith an attached squirrel cagefan. This moves air from thetop of the puck to the bottom.Around the fan assembly is ahousing and a rubber bumper.The entire structure is verylight with a mass of only 183grams without the battery and300 grams including the 6-voltrechargeable battery.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.A. Kick Disc base with 6-volt motor wired with a switch on the bottom (not shown). The grids provide air flow downward and outof the disc. (112 grams with the motor)B. The rubber bumper that protects the plastic from impact. (11 grams)C. The top of the disc with the air
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