1997-2006 Academic Years
10 November 1998: Larry Alofs [Kenwood Academy HS]
He showed the Pasco Mini-Launcher (circa $125 in 1997 catalog). [http://www.pasco.com] The assembly has a spring and gimbals that allow it to be aimed. He did not initially know the speed of the ball upon launch, so he pointed it up--it traveled 143 cm high (launch speed: 5.3 meters/sec. With photocell gates it was measured to be 5.27 meters/sec) At a launch angle of 60o to the horizontal we calculated a rise time of 0.47 seconds, or a flight distance of 2.48 meters. After launch the ball hit a pan at the distance of 2.48 meters. Next he tried 60o and the distance was again 2.48 meters. Next he adjusted to 45 degrees, and fired. Did it again hit the dish at 2.48 meters?? Nope!!!
09 November 1999: Bill Blunk (Joliet Central HS)
showed us how he involved his students in projectile motion using an air-powered rocket (http://www.arborsci.com Arbor Scientific, 2000 Catalog). He uses two boards, hinged at one end, with the launcher mounted on the top board. The top board can then be tilted to a desired angle by turning a screw down against the bottom board, thus controlling the angle of projection for the rocket (handout). To get rocket altitude, Bill lays out a 50 m base line (using trundle wheel), and then they sight on the rocket at its peak altitude using a height finder (Estes or Flynn catalog), which easily captures the angle. Bill "fired" the rocket using a bicycle pump to pressurize the launcher, but we couldn't do it outdoors because of wind and darkness, so he covered it with a box (to prevent impact with the room ceiling). Pow! It worked!
07 December 1999: Carl Martikean (Wallace School, Gary)
described how to make a 2 liter pop bottle stomp rocket. See the website http://www.sciencetoymaker.org/airRocket/index.html ... and someone remarked that the active ingredient [energy source] for this device is your foot!
9 October 2001 David Dunlop (Great Lakes Space Sport Foundation;
Telephone Number: 708 -
Guest Presentation on Rocketry [see http://www.rocketry.org/links/ and http://www.rocketryonline.com/]
He described an outgrowth of the the Wisconsin Rockets for Schools educational program based upon rocket launches, which was begun in Sheboygan WI (a city on Lake Michigan 100 km North of Milwaukee and 300 km North of Chicago) in 1991, receiving initial support from the State of Wisconsin and Michigan Technological University in Houghton (UP) MI. A parallel program, Michigan Rockets for Schools, has been operating out of Muskegon [UP] MI since 1997. This launch site was used for Meteorological Rockets, such as the Super Loki rocket http://www.phy.mtu.edu/rocket/superlok.html, that rose up to a height of 50 km, had a maximum speed of about 1500 meters/second [about Mach 5], and produced a maximum thrust of about 110 g's. Meteorological rockets are no longer used in meteorology, their role in determining upper air wind velocities being replaced by detection of dispersion of signals from orbiting weather satellites.
The educational program rocket launch is held annually during the third week of May on the pier in downtown Sheboygan, about 60 meters into Lake Michigan. The rockets are accelerated to a speed of about 250 meters/second using a motor that produces about 600 Newton-seconds of impulse. They rise over the lake to a height of about 700 meters, and are retrieved by recovery teams --- 95 % of them fall into the lake, and 5 % onto the nearby shore. The rockets employ standard "low explosive" motors that are inserted by professionals, who also launch them.
They use the standard rocket propellant [http://www.answers.com/topic/ammonium-perchlorate] Ammonium Perchlorate, NH4Cl04, with a category I rocket motor. According to FAA Classifications, A, B, C, D, E, F, G are "model rocket" categories, whereas H, I, J, K are strictly licensed "high powered rocket" categories. David said that they do additional launches with more powerful rockets [ie, K] on that date---one recently launched rocket went up around 3 km and drifted inland under prevailing winds, and landed in a K-Mart parking lot on the other side of town! David also described balloon launches, which may rise to a height of 30 km before the balloon bursts, a parachute opens, and the payload drifts to a "soft landing" somewhere on earth.
Student groups may enter the contest by ordering a rocket kit, which consists of a phenolic-impregnated cardboard tube about 2 meters long, assorted vanes, a payload bay about 50 cm long, etc. The rocket superstructure has a mass of about 2 kg, the rocket motor [attached onto the rocket at launch by professionals] is about 0.5 kg, and a rocket payload can be as much as 2 kg. The rocket automatically depressurizes at apogee, and a parachute opens to keep the payload from crashing down. There are speedboat recovery teams to fetch the payload, as well as teaching teams to answer questions about rocketry.
The payload, can be virtually anything that fits inside the tube, and is limited only by expense and durability. Students have put in accelerometers, anemometers, CPL devices, GPS sensors and transmitters, etc. It is important that the payload be waterproof, since the landing usually occurs over water. Many groups collaborate with local Amateur Radio Clubs, since those groups are good scroungers, are knowledgeable about electronics, and usually quite interested in the project. Each team makes an oral presentation after their launch.
David described a sport rocketry program that is based upon sound educational principles. The goal is to produce the excitement and enthusiasm of a sporting event, while maintaining a strong educational mission. For additional details about the program you may call David Dunlop at (708) 848-6605.
The rocket launches in the 1958 by future NASA Rocket Engineer Homer Hickam [http://www.homerhickam.com/new1.htm] and his fellow students in Coalwood WVa are beautifully described in the book [http://www.homerhickam.com/books/rb.shtml] and film [http://www.cnn.com/SHOWBIZ/Movies/9902/18/review.octobersky/] October Sky. Their home-made rocket engines were comparable in thrust to the "high powered rocket" categories I - K, and students would certainly not be allowed to build such rocket engines from scratch today. Lower category "model rocket" engines are available at hobby stores today for use under strict supervision.
Winifred Malvin (Carver School) NASA Handout: Rockets. A
Teacher's Guide with Activities in Science, Mathematics, and Technology
We started with three sheets of paper of three different colors, and a set of directions to make paper rockets. We cut a 4 cm by 28 cm strip of paper, and rolled it diagonally around a pencil, taping it in three places. We then removed the pencil, cut off the ends of the paper, put fins on one of the ends, folded the other end over and taped it shut, and inserted a straw. The rocket was launched by blowing through the straw. Alternately, you could blow up a balloon and attach it to the straw for a more vigorous launch. Questions on the performance of the rocket, the function of the fins, the number of fins needed, and their position on the rocket are discussed the NASA Handout. Good stuff, Winifred!
08 October 2002: Don Kanner [Lane Tech HS,
Physics] Rocket Ship Physics
Don simulated the motion of a rocket ship in free space by blowing up a balloon and releasing it above the table. The balloon expelled air and was propelled forward, in analogy to a rocket ship that expels burned fuel and is pushed forward. Don reasoned that, when gas is expelled at a constant rate, the rocket ship will have an increasing acceleration, because its mass is continually decreasing. The rate of change of acceleration with time, Da/Dt, which is commonly called the "bump" or "jerk", is non-zero in this case. He asked us how to handle this case of changing acceleration. Porter Johnson commented that, while higher derivatives of position with respect to time can always be calculated, in Newtonian dynamics, nothing beyond the second derivative [acceleration] plays a fundamental role. For rocket dynamics in free space, it is sufficient to apply conservation of momentum, since the sum of the momenta of the rocket and of the expelled fuel does not change with time. The forces between the rocket and fuel being expelled are equal and opposite, by Newton's third law, and thus the total momentum is conserved. To explore the dynamics let m(t) be the mass of the rocket ship, which decreases with time. At the beginning of a short time interval, the rocket has mass m and initial velocity v, whereas at the end of the time interval its mass is (m+Dm) and its velocity is (v + Dv) --- note that Dm, the increase of the rocket mass, is negative!! The expelled mass, - Dm, has speed (v - vex), where the relative speed of the expelled gas relative to the rocket is vex, the exhaust velocity. The requirement of momentum conservation is
If a rocket of mass m = 1000 kg is expelling gas at the rate of 10 kg/sec, and at an exhaust velocity of 500 meters/second, relative to the rocket, the thrust produced by the rocket has the constant value of 5000 Nt. The mass of the rocket at time t is m(t) = 1000 - 10 t in kg, so that the acceleration continually increases:
|Time (sec)||Rocket Mass (kg)||Acceleration (m/sec2)||** Speed (m/sec)|
23 September 2003: John Scavo [Evergreen Park Community
John constructed a rocket, complete with nose cone, by wrapping a sheet of paper around an empty film canister to form a rocket, according to the instructions given in one of his lessons on the SMART website, Film Canister Rocket: http://mypages.iit.edu/~smart/scavjoh1/lesson2.htm. As explained there, the film canister is at the base of the rocket, and its cap is at the very bottom. Having assembled the rocket, complete with nose cone, he put 1/4 tablet of Alka-Seltzer®, then added water, then put the cap back on, and put the rocket on the launch pad (table top). The cap popped off within a few seconds, and the rocket shot upwards to the ceiling. In fact, it was hard to avoid premature 'ignition'. He 'fired' the rocket several times, and used an alternative fuel --- baking soda and vinegar.
John has made the transition from teaching science to teaching web design classes in the business department. He was able to make this transition because of his experiences as a student and then as a staff member in our SMART program [http://mypages.iit.edu/~smart/]. He said that, unlike in his "former life" as a science teacher, he routinely runs into students who know more than he does about web design. After some adjustment, he has learned to get them to share their knowledge with him. He said that "hands on" teaching is called "quantum learning" in his new department. John recounted his childhood experiences with the Estes Rocket, [http://www.estesrockets.com/store/rockets/educator.html] which involves using a pressurized can (then filled with Freon®) for the launch. He also explained the meaning of an (apocryphal?) remark allegedly made by Neil Armstrong while he was on the moon in 1969. Finally, he mentioned matchstick rockets: http://www.matchstickrockets.com/.
John, your rocket really hit the spot--on the ceiling! Cubs Rule! [at least temporarily]. We enjoyed your lesson -- and thanks for reminding us of our own childhood adventures!
19 November 2002: Wanda Pitts [Douglas
Wanda passed around the handouts A Remarkable Race, as well as Scientific Method: Good Clean Fun from the book How to Do Science Experiments With Children: Grades 1-3 by Joan Bentley, Linda Hobbs [Evan-Moor Educational Publishers 1994] ISBN: 1-5579-93378. Wanda convinced us that soapy water has less surface tension than ordinary water, by having us build a "soap boat", and seeing it "shoot" across the water. We made the boat by cutting a small triangle out of a a piece of corrugated cardboard, then putting a small notch on the triangle base. We then put the boat flat on the surface of water in a bowl, with the notch near the edge. We carefully placed a drop of dishwashing liquid in the water where the notch was located, and saw the boat speed across the water! The molecules of the dishwashing fluid are attracted to water, and the dishwashing liquid breaks the surface tension, causing a ripple effect that pushes the boat forward. As an additional illustration, we sprinkled pepper over the surface of a bowl of water. When we added a drop of dishwashing liquid, the pepper moved away from the center and toward the edge of the bowl of water. For more details see the Nerdscience.com website [Be the rocket scientist you always wanted to be!], called Soap Boats - The Science of Surface Tension, http://www.ed.gov/pubs/parents/Science/soap.html as well as the presentation by John Scavo in the Math-Physics SMILE meeting of February 1, 2000. Very dramatic and exciting, and educational as well. Good show, Wanda!
07 October 2003: Bill Blunk [Joliet Central HS,
physics] Paper Match Rocket and More
Bill constructed a launching pad using a piece of cardboard paper, and a paper clip bent to support a light object leaning against it [a paper match stick -- wooden matches are too heavy to work]. First he tried to launch the paper match just by putting it on the launching pad and lighting it. The launch fizzled, because the match just sat still and burned. Why didn't it go flying away? After some discussion it was decided that there was no net impulse given to the paper match in this process, since the exhaust gases from the match were sent in all directions. One must find a way to direct the flow of exhaust gases to provide a net impulse. So, Bill wrapped the head of the paper match several times with a small piece of aluminum foil, pressed it tightly at the top so that exhaust gases would come only out the bottom, and placed the paper match head-up onto the launch pad. Bill then lit another match and held it under the wrapped head of the match on the launch pad. There were audible hissing sounds from inside the foil, as the match head ignited and (anaerobic) combustion began. A split second later, the paper match jetted off the launch pad, and bounced off the ceiling. Details on construction and operation were given in last week's summary. Bill, you really set things on fire, intellectually speaking!
Bill also presented an extension of last week's lesson on balancing an egg at the Autumnal equinox. In particular, he pretended to "balance" a golf ball on a horizontal board. Of course, one would not expect the ball to move, because it is round -- unlike an egg placed on end. and it did not move. Then, Bill slowly tilted the board up on one end, making an angle of about 30° to the horizontal -- and the golf ball still did not move! Amazing! After extensive cross-examination by the group, Bill finally admitted that the experiment was a hoax. Namely, the golf ball was spherical in shape, but its center of mass lay significantly below the geometrical center. Bill had made his annual pilgrimage to Amazing Toys in Great Falls MT. This item can also be ordered through their website http://www.amazingtoys.net. Very slick, Bill!
-- which means Snail
Race auf Deutsch. Bill called attention to a very
race between trained snails which was held in Cremonia (Alpine
last Summer. By holding a piece of lettuce and crawling in front
snail, the winning snail trainer (female, age 11) had coaxed the snail
1 meter in 450 seconds, corresponding to an average speed of
mm/sec. As prize for this victory, she and her pet snail
lettuce bowl. This speed is significant, in that it is
greater than a
typical drift velocity of electrons in a conducting wire, even
high currents. And, think of how proud the winning team must be
in this annual
event, described in the (Deutsch) website (with pictures) given
Fascinating topics and spectacular stuff, Bill!
09 December 2003: Fred Farnell [Lane Tech HS,
physics] Rocket Balloons
Fred took a long, collapsed balloon, and inflated it by inserting a special straw and blowing. Then he released it into the air. It zoomed around the room, making a "screaming" sound. Just for amusement and edification, he sent off several more balloons, with similar effect --- except for the one that exploded during inflation. This is an ideal party favor, which Fred had obtained from The Party Corner®, in Orland Park Shopping Center. It was described on the package as follows:
Referring to his presentation at a previous SMILE meeting, Fred promised that he would bring his daughter's old tennis shoes to SMILE in the near future, since she is nearly ready to donate them to us for scientific study. And, it's about time for her to wear winter shoes!
Those rockets really took off! Thanks for showing us, Fred.
20 April 2004: John Bozovsky [Chicago Discovery Academy: Bowen
Rocket Altitude Measurement
John is a physics teacher who, for decades, has motivated his students' interest in physics by getting them involved with model rockets. Why can design construct, and send a model rocket to the highest altitude, h? Which raises the question: how can students measure h for their rockets? (handout) John explained that, in practice, it is rather difficult to measure h, since the rocket seldom goes straight up from the launch point, but tends to wander off in some direction or another. With the aide of a colorful 3-D scale model to show the geometry of the situation clearly, he showed us how to find h using two observers, A and B, positioned at each end of a baseline of length AB, laid out on the floor (presumed level) ahead of time. Two large circles (about 1.5 meter radius) are drawn on the floor centered at A and B at each end as well. When the rocket reaches its highest altitude (zenith) at the position, Z, in space, observer A uses his Astrolabe [http://www.astrolabes.org/astrolab.htm] to record the angle, c, above floor level of the rocket, as shown:
Z (rocket zenith) Z (vertical plane) . | | . (different vertical plane) . | | . . | h h | . . c | | d . A--------X X-------- B(X is the point on the ground directly below Z. Similarly, observer B uses his astrolabe to record angle d.) Observer A -- immediately after recording the angle c on his astrolabe -- moves his astrolabe vertically downward to point toward X at floor level, and places a mark on his circle to enable measurement of angle a, with a protractor, which he does, as shown in the diagram below. Similarly, B marks his circle and measures angle b.
X (projection of location of rocket . . maximum height onto the ground) . . (plane of ground) . a b . A--------------BNote that, from the Law of Sines,
Information on the Astrolabe is given on the Encyclopædia Britannica website: http://www.britannica.com/clockworks/astrolabe.html. Seel also A Treatise on the Astrolabe by Geoffrey Chaucer [http://art-bin.com/art/oastro.html], which is considered to be the oldest technical manual in English.
The Estes Rocket Kits, which include the astrolabe (angle measuring device) may be ordered at the following URL: [http://www.hobbylinc.com/prods/t_est.htm].This rocket launcher is part of the Physics Van demonstration exercises being developed at Chicago State University for delivery to and use in local high schools. for details call Prof Mike Mimnaugh at Chicago State University (773) 995-2180.
John, this really is about rocket science! Thanks!
04 May 2004:
Chris Etapa [Gunsaulus
Academy] Force and
Motion Illustrated with Rockets
Chris made a mortar tube about a meter long from a piece of poster board, rolled up to a diameter of about 15 cm -- which was large enough to hold a small inflated balloon. We divided into groups, each group blowing up a balloon and holding in the air without tying it. We then taped a Styrofoam® cup over the end of the balloon, to serve as a nose cone. While still holding it shut, we put the balloon into bottom of the tube, and then let it go. The balloon rocket took off, and went across the room! We discussed how Newton's 3rd Law (action-reaction) was involved.
Chris -- with a little help from Terri Donatello -- then showed us how to make a straw rocket. We again blew up a balloon, and taped a soda straw to its side. A long cord, several meters long, was threaded through the straw and then stretched taut across the room.. When Chris let go of the balloon, it zipped across the room, the straw traveling along the string that served as a track for the rocket.
Chris then showed us how to make an Alka Seltzer® rocket. She took a 35 mm film canister (with its snap-on cap) and taped a paper nose cone onto its bottom. She put some vinegar (dilute acetic acid in water) into the canister, added 1/2 of an Alka Seltzer® tablet, put the cap on, and turned it upside down (nose cone up) on the floor. Carbon dioxide gas, which is produced by the chemical reaction NaHCO3 + H+ ® Na+ + H20 + CO2 (gas), causes a pressure increase inside the canister, and the cap is blown off. The rocket goes straight up, and very fast! Pat Riley pointed out the importance of the ideal gas laws in explaining the pressure increase that produces the launch. For more details see Film Canister Rocket by John Scavo on the SMART home page at location http://mypages.iit.edu/~smart/scavjoh1/lesson2.htm.
Chris distributed the following questions for discussion:
This was a blast! Very good, Chris!
28 September 2004: Betty Roombos [Gordon Tech HS,
Betty found a very nice Constant Speed Motion Car in a Science Kit catalog: http://www.sciencekit.com/: [Item 66213-1, cost $7.50, requires 2 C-cell batteries. After she obtained the car, she tested it and found that it traveled at a rather constant speed -- true to its name. We found that it moved across our classroom floor in a rather straight path with a speed of 40 cm/sec. Very nice! We also noticed that, when the car ran into the front wall the front wheels climbed up the wall. The car flipped end-over-end, and went back to in the opposite direction. The car was smart, as well as reliable! Betty gave us a handout describing the Constant Speed Experiment for her students, which used a Pasco Recording Timer that produced dots at constant time intervals on a strip of recording tape attached to the car. Her students constructed graphs of distance vs time and speed vs time to test for uniform speed. Now, that's a hot car! Thanks, Betty!
26 October 2004: Babatunde Taiwo [Dunbar
Understanding Car Crashes: It's Basic Physics (video)
Babatunde showed a 22 minute video illustrating the concepts of inertia, impulse, momentum and force in car crashes, which was prepared by the Insurance Institute for Highway Safety [call (703) 247-1500 or go to the website http://www.highwaysafety.org/], which may be ordered from Arbor Scientific from the website http://www.arborsci.com/Products_Pages/Multimedia/CarCrashBuy1.htm. Here is an excerpt from that website:
"What happens to vehicles and their occupants in crashes is determined by science. "You can't argue with the laws of physics," says Griff Jones, award-winning high school physics teacher, who goes behind the scenes at the Institute's Vehicle Research Center to explore the basic science behind car crashes: inertia, crash, forces, momentum, impulse, and a lot more."The following points were made in the film.
Very informative, Babatunde!
09 November 2004: Roy Coleman [Morgan Park HS,
Roy announced a rocket launch (outdoors) at the Williams Science Center of Chicago State University next Monday, 15 November 2004. The rocket launch will be done by veteran SMILE participant John Bozovsky and Mel Sabella of Chicago State University: Tel 773-995-2172.
Happy (rocket) trails, Roy!
14 December 2004: Arlyn van Ek [Illiana Christian HS,
Air Zooka™ Vortex Launcher
Arlyn showed off his new physics toy, the Air Zooka Vortex Launcher, which he had ordered from a recent Teacher Source Catalog [http://www.teachersource.com/] by Educational Innovations Inc for around $15. Here is a description of the vortex launcher from that source:
"This amazing device launches a powerful vortex of air up to 20 feet. Powerful enough to blow out a candle from across the room! Safe for classroom use because it launches no projectile, only a strong puff of air. Easy to use and requires no batteries. Colors may vary."We tested the device by lighting a cigarette lighter in the back of the room, and then blowing it out with the vortex generator from across the room, more than 6 meters away. It worked! Arlyn also got a Wizard Stick Fog Generator from that same source. Similar devices are available at the K-Mart ZeroToys website: http://zerotoys.com/newsite/products.htm, and to obtain the best price one can use Google-Froogle [http://froogle.google.com/].
Great gadget! Thanks , Arlyn!
29 March 2005 Larry Alofs [Kenwood HS,
Larry showed us this device, which is a substantially modified version of one presented by Tom Senior. He used a 2 meter PVC pipe of inside diameter about 38 mm (1.5 inches), with plastic caps for the ends. Near one end there was a T-connection to a vacuum pump. He inserted a ping-ping ball, tilted the pipe so that the ball went down to the end near the vacuum pump connection, and capped both ends. He found that the new, translucent caps on Pringles™ cans worked very well for capping. After he turned on the vacuum pump and let it run for a minute or so, the cap was visibly deformed. When he punctured the cap at the lower end, there was an explosive POW! --- the ping-pong missile shot out the other end, and SMASHed against the opposite wall. Very impressive display of launching power! The launch velocity of the ping-pong ball would surely be less than the velocity of sound, but it appeared to be quite fast, since we could not follow its trajectory, and the POW! and SMASH! seemed simultaneous. Larry then set up the apparatus with the bazooka aimed directly at a cardboard box, and launched it again. The ping-ping ball shot through both sides of the box, and smashed against the wall. Now, that's a really powerful serve!. Thanks for the powerful display of forces arising from air pressure, Larry!
20 September 2005:
Bill Shanks (Joliet Central HS and Joliet JC physics,
Balloons and aircraft.
Bill brought in a great toy that he had obtained at Walgreen's --Rocket Balloons -- which are large, long balloons with a hand pump. When fully inflated with the pump, a balloon was about 1.2 meters long and about 8 cm in diameter. When the balloon was released, it flew around the room and remained in the air for about 7 seconds, while making a squawking noise. Bill discussed this rocket flight in terms of conservation of momentum. As the air inside the balloon is expelled, it gains momentum (to the left). This change in momentum of the expelled air is equal and opposite to the change in momentum of rocket balloon, which moves to the right.
Bill then asked whether we thought a rocket would work better in the atmosphere (ignoring friction and gravity) or in empty space. Bill thought that it would work better in the atmosphere, although most of us did not agree. Bill also described lift, and questioned whether Bernoulli's principle played a crucial role in explaining flight. Bill discussed the work of Physicist David Anderson of Fermilab and Aeronautical Engineer Scott Eberhardt of the University of Washington. For details see The Newtonian Description of Lift on a Wing: http://home.comcast.net/~clipper-108/Lift_AAPT.pdf. They conclude that the Bernoulli effect does not account for enough lift to hold the plane in the air. Instead, lift occurs because the wing pushes the air down, and by Newton's Laws the air pushes up on the wing.
Bill then described the "Ground Effect" in flight of a plane, When a plane flies just above a smooth surface (such as a body of water), the air is pushed downward and actually compressed. This layer of compressed air under the plane provides additional lift. This effect is especially important for flight of Helicopters. For details see the Wikipedia article Ground Effect in Aircraft: http://en.wikipedia.org/wiki/Ground_effect.
Fred Schaal mentioned that tips on propellers of some aircraft actually move near or above the speed of sound. For details on the Thunderscreech airplane, see the website http://hsfeatures.com/features04/xf84hbd_1.htm.
Bill also discussed kite flying in the wind. The kite catches the breeze and pushes it downward, thereby providing lift to the kite. The purpose of the tail is to keep the kite properly oriented toward the wind, and to provide stability in flight. For details see the NASA article Kite Launch and Flight: http://www.grc.nasa.gov/WWW/K-12/airplane/kitefly.html. Great stuff! Thanks, Bill!
13 December 2005:
Erik Jurgens [Joliet Township HS,
Projectile Motion Made Visible
It can be obtained from K-Mart® for about $10. A similar toy can be found at the Dollar Store®. It is a plastic air gun -- about 60 cm long and 5 cm in diameter --which shoots a Nerf™ projectile. Erik attached a streamer (about 2 m long )to the projectile. When the gun is fired, the path of the projectile is made highly visible, thanks to the streamer which traces out a smooth, roughtly parabolic path. An excellent invention, Erik!