`Physics Lab RocketsJoseph Dogadalski             Austin Community Academy H. S.                                231 N. Pine                              Chicago, IL 60644                               312-287-5000Objectives:To promote interest in laboratory work at the beginning of the high school year.To discover some qualitative variables involved in making a balloon rocket on a string.To promote team activity and cooperation by preparing for and having a balloon rocket contest.To shoot a model rocket outdoors and calculate its altitude.Three levels of interest:1. To calculate rocket's altitude by using angles, triangles, and proportions.2. To compute its altitude by assuming its path is perpendicular to the eye level plane above grass and use the tangent function. 3. To assume rocket's trajectory is a straight line at a non-right angle to the eye level plane and to have each team measure the angle of elevation at two distances in line from the launch point and move over to another line and do the same (see wire model).Materials:     FOR EACH GROUP: A picture of a line hanging from ceiling to lab desk with a straw and a balloon on it; roll of Scotch tape; straw; packet of a dozen assorted balloons; a monofilament line hanging from ceiling to be attached by each group to their lab station in the classroom; two sighting instrument kits made up of a ruler with a picture of an upside down protractor on it and a plumb line (string and a weight) taped to the point of vertices on the protractor.      FOR THE CLASS: A not too windy day; a grass field 30 by 100 meters; one or two identical model rockets ready to launch; half-dozen rocket engines that will propel the model to a height of 20 to 30 meters; three ropes with knots at 5 meter intervals 30 to 40 meters long, ready to be stretched out at various convenient angles from the launch point; a coat-hanger wire model of a tetrahedron in which the vertices (corners) are held together by rolled up rubberbands and able therefore to be adjusted to various angles. Strategy:INTRODUCTORY ACTIVITY: Blow up balloons and let them fly out of hand; watch their random motions; students will thread the prepared line from the ceiling through a straw and tie it to the lab top; tape blown up balloon(s) to the straw and let them fly;      While the groups are experimenting, the teacher can walk around and give clues to "What's happening?".  Discuss: action-reaction, conservation of momentum, pressure in an uninflated and inflated balloon, catastrophic punctured balloon, and the conditions needed to make a balloon rocket.  Also the teacher will walk around with the wire tetrahedron and show the possible flight paths of the model rocket to be fired, the geometric line of sight, and the angle of elevation to be measured.      Students are to be preparing their design for the contest "shoot off" at the "teacher's shooting range".  Maximum height from floor wins.  After experience with a half-dozen shots, students should be ready for the contest.      BALLOON CONTEST DATA (best of two shots)     Trial                         1           2         (height from floor)      Team A,B,C,...(circle one) ACTIVITY: After the contest the whole class will go out to the grass field to shoot the model rocket.  Before the rocket launch, student groups will learn the use of their sighting instruments.  Before each firing, teams will pick one station on the stretched out ropes radiating from the point of launch.  If a student group wants to launch the model rocket, they must learn the 14 safety points of the model rocket society which come with the engines.  Otherwise the teacher should always launch the rocket.                                                               MEASUREMENTS   TEAM A,B,C,...    Distance of station from          Angle of elevation   (Circle one)      launch point on line 1,2,3.   First launching   Second  "   Third   "   ...Conclusions:     Rockets should reach a consistent altitude by using the same model, same engines, and the same launch angle.  Students will learn the safety points of launching a model rocket.      On the first level of interest, students, by drawing similar triangles withthe measured angle of elevation, should be able to calculate the altitude by making a proportion.      On the second level, students should determine the altitude by making the tangent of the elevation angle equal to unknown altitude divided by the distance from launch point and solve the equation.      On the third level, a group will divide into two and stand in two locations on one of the rays (knotted ropes).  They will measure two elevation angles and draw an oblique triangle the base side being the distance between their positions on the ray.  Having two angles and the included side of an oblique triangle, the group can determine a second short side by the "Law of sines".  Using this side, the closer elevation angle and the sine function, students will be able to figure out the altitude of a rocket with any non-right angle trajectory to the level plane.  In all these cases, a good figure is worth more than all these words; but especially the wire tetrahedron model will be useful in showing the various possible trajectories in three dimensions.      A measurement of time (seconds) opens up the whole world of motion.Evaluation:     Student grades will be based on scale drawings of triangles, angles of elevation and the appropriate calculations.  Also, the answers to the questions below will be considered. Questions:1. When does a balloon act like a rocket?2. Name some variables that influence the balloon's flight?3. 20 is to 40 as 60 is    .4. Similar triangles have the same shape but a different    .5. Would a real rocket work better in outer space?6. A real rocket's mass is mostly     .   `