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Figure 4.3 2. Balloons

Figure 4.3 2. Balloons with Gliders [] Release a light glider from a balloon with a novel ice-switch time mechanism. What you will need • Balloons filled with hydrogen. You could fill them with lab grade H2 or He or prepare your own. • Plastic drinking straw • String, masking tape & scissors • Paper plane or cheap toy glider • Freezer • Impact heat sealer or hot glue gun Here’s how 1. Cut a plastic drinking straw into about 3 cm (1.2”) lengths. Seal one end of each using a kitchen heat sealer or you could use a hot glue gun. Check that it is water tight. Figure 4.4 2. To prepare an ice-switch: Insert a piece of string into a plastic drinking straw with a length protruding from the straw and fill with water (Figure 4.4). Place it in an upright position in the freezer and leave for approximately 30 minutes to allow the water to freeze. 3. Remove from the freezer, note the time. Let it hang suspended on the string outside in the sun (the same conditions that will exist under the floating balloon). Note how long it takes for the ice to slip out (Period A). Repeat the experiment several times to obtain a more accurate value. Figure 4.5 37

4. Decide on the time lapse after which the glider should be released from the balloon by the ice switch, e.g. 1 minute after launching (Period B). 5. Determine the waiting time before the balloon should be launched (Period A minus Period B). Example: Period A : from freezer till ice slips out : 7 minutes. Period B : from launching to releasing of glider : 1 minute Period A - B = time to wait before launching the balloon: 6 minutes. 6. Fill a balloon with hydrogen gas, prepare an ice-switch and tie the ice-switch string to the balloon. Tape the ice-switch straw to the glider with masking tape (Figure 4.5). 7. Launch the balloon at the calculated time, keeping your bicycle at hand to retrieve the glider when it lands. Enjoy! Figure 4.6 B. Making Hydrogen go Bang! There are many ways in which hydrogen’s exothermic reactivity can be visually demonstrated. Activities range from the meek and mild hydrogen pop in a test tube to unsafe combustion in glassware. I once saw a teacher filling a glass milk bottle with hydrogen gas. He wrapped it in a towel (just in case . . .) and ignited it. He was lucky - the bottle did not shatter. Filling glass containers with hydrogen and igniting the gas is something one should never attempt. Please steer clear from this activity. Safety / Risk Assessment ! Hydrogen is not flammable on its own. It requires oxygen to combust but this can happen over quite a wide range: 7 to 75% in hydrogen ! Stick to the instructions and quantities as advised. ! No matches, sparks or flames should be brought close to the hydrogen balloon storage area. ! Keep all flammable and combustible material away from the working area. ! Wear eye and ear protection as well as a lab coat. 38