EXPERIMENT #2: Controlled Propulsion

Supplies:

balloons of various sizes and shapes

plastic drinking straw (cut to size)

50 feet of thin string

masking tape

As you know, rockets travel in a straight line. This is because the escaping gasses are very carefully controlled and the rocket is well balanced. To make your balloon travel in a straight line, perform the following experiment:

Procedure:

1. Measure off a distance of at least 24 feet.
2. Slide the drinking straw onto the piece of string.
3. Have two students hold each end of the string taut at shoulder height. (Or tie between two stationary objects, i.e. chairs)
4. Place two loops of masking tape onto the straw.
5. Blow up a long balloon to its maximum capacity. Hold tightly onto the neck of the balloon so that no air escapes, and attach the balloon to the two pieces of tape. The neck of the balloon should be parallel to the string.
6. Release the neck to let the air rush out.
7. Repeat above six steps with other shapes of balloons.

Expected Results:

The balloon should propel itself along the string.

Questions to ask the class:

1. If a small and large balloon were both inflated to their maximum capacity, which would travel further? [The larger balloon would travel the furthest because it has the most fuel .]
2. If a small long balloon and a large long balloon were both inflated with the same volume of air, which would travel further? [The small long balloon would travel further because it has more pressure built up as well as less mass to move.] Would the same occur with round balloons? [Yes]
3. If a long balloon and a round balloon were inflated with the same volume of air, which would travel further? [The long balloon would travel further because it has a more aerodynamic shape.]