Return to Physics IndexPhysics Lab Rockets

Joseph 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 with

the 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.