Balloon rocket science experiment-How to set up the investigation for students in a classroom.

• This is a fabulous and fun experiment, aimed for Years 8/9/10, it involves Newtons third law (action and reaction), fair trialling, and measuring skills. Equipment: Balloon, drinking straw, peg, Sellotape, measuring tape, string, pump, stop watch or ruler, two retort stands with boss heads, clamps or two chairs. Students should wear safety glasses if there is a chance of the balloon bursting.
• Make sure that there is enough uninterrupted space for the string to stretch across the room, about 9-10m is a good length, shorter lengths are fine.
• By keeping the distance constant and measuring the time (dependent variable) of the balloon rocket to get to the end (the run), the students are effectively measuring the speed. Or students could measure distance travelled versus the size of the balloon.
• Time a run or measure the distance gone with a different volume of air in the balloon, students can measure the circumference of the balloon with a tape measure (independent variable) or they could count the number of pumps. Start with a small balloon and finish with a big balloon in regular circumference sizes, eg. 30, 35, 40, 45 cm …
Check in with your students’ knowledge of the scientific inquiry method. Frame the investigation using scientific language: What makes a trial a fair trial? Use opportunities to introduce or reinforce vocabulary such as hypothesis, prediction, mass, and force.
Make sure that the students discuss why their predictions were accurate or inaccurate and that they generalise their results. Ask What does your experiment teach you about the physical world?
Discussion and science ideas
• Plot a line graph of Run time (s) versus size of rocket balloon (cm), explain the relationship between the two variables.
• Results and observations will vary. (As long as the straw can move freely along the string, the balloon will shoot across the room. The air trapped inside the rocket balloon is under greater pressure than the air outside [that’s why the balloon “blows up”]. When this pressurised air is allowed to escape, it rushes out of the balloon. [Newton’s third law states that to every action there is an equal and opposite reaction. The balloon moves in the opposite direction to the escaping air.] The rocket balloon works the same way as you would if you were standing on a skateboard holding a heavy backpack. If you throw the backpack one way, you roll the other way. In this case, instead of a backpack, the rocket balloon “throws” air one way and jets off the other way.)
• The more air there is in the balloon, the more force it will have and the faster it will move. If you decrease the number of pumps (lower the air pressure), the balloon has less force and will go slower.
• Results will vary. Shape probably doesn’t make much difference, although some shapes will need more air to fill up and other shapes will release the air faster (more force!). A large balloon will be affected by the air and wind more than a long skinny balloon, but in a classroom, the amount of air you put in each balloon is probably more important than air resistance.