Paper Hot-Air Balloons
Paper hot-air balloons are a great activity for understanding buoyancy, as well as providing an opportunity for inquiry. While there are numerous excellent ways to make them, the method I have used seems reliable, cheap, quick, and flexible.
A
simple cylinder is constructed of 8 pieces of colored, standard tissue
paper (approx. 14"x 28"). 4 panels are made, each of 2 pieces
of tissue paper glued end-to-end. Then the 4 panels are glued side-to-side
to make the cylinder. Finally, one piece is cut to be a square, (a good
problem for kids, but easily solved by folding one corner across to the
opposite edge and removing the remaining strip) and glued on one end.
Each edge of the square matches one side of the "square cylinder".
This can be completed easily in one day by almost any age student.
Glue stick is the best way to attach pieces with minimum weight (and least mess), while white glue will work, too. Holes can be repaired with a small piece of paper glued over the problem. Then add a few, medium-sized paper clips, evenly spaced, around the bottom to help keep the balloon upright. You can use a wood fire for heat, which I channel through a conical metal device that is meant as a charcoal starter.* (Protect the ground with a metal tray, or garbage-can lid.) Several people hold the balloon upright over the heat and when it seems full of hot air: "Away we go!" We have had balloons fly over schools and also travel substantial distances, sometimes too far! Since the upward force is produced by the difference in mass between the balloon and the air it displaces, calm, cool days are best because the displaced air is denser than on a warm day, thus producing a greater buoyant force.
With Connect's emphasis on Inquiry, I recommend letting the students repeat the lesson with balloons of their own design. Now they can predict and test their hypotheses, regarding shape as well as size, or other design variables. The best balloon I ever saw was a sphere that a student made out of eight equilateral triangles! He glued 4 triangles edge-to-edge to approximate a hemisphere, repeated that for a second hemisphere, and then connected the open ends together to produce the equator. (The closer to a sphere, the greater the lift, since a sphere displaces the most air for a given amount of paper--another good geometry lesson.)
*There is certainly a safety issue, in that the paper can ignite. It may be possible to get a cylinder to fly with a large, powerful air-drier. I have had two or three balloons catch fire, out of the hundreds I have helped make. This has happened always on windy days when it is hard to hold the balloon straight and centered over the fire-cone. Just let go and it will burn up in a few seconds while it is still in the air.
--
Dr. Tom Ostwald, Director
UCSB School-University Partnerships &
South Coast Science Project
Graduate School of Education
UCSB, Santa Barbara, CA 93106
(805) 893-5663
tom@education.ucsb.edu
