The Hot Air Balloon Challenge
By Emily and Michael
Materials
-an eight gallon plastic bag
-two pipe cleaners
- a tinfoil basket (size varied based on the trial)
- cotton balls
- five mL alcohol
-a match to light the alcohol
For our fourth (and final!) trial, we used:
-an eight gallon plastic bag
- four pieces of wire about eight inches long
- a tinfoil cup/basket
- two cotton balls
- five mL alcohol
- a match to light the alcohol
Design
Because the fuzz on the pipe cleaners was flammable, we burned it off beforehand, which left just the wire from the pipe cleaners, and we also used three cotton balls (so as to not have a ton of alcohol just on one cotton ball). We used 5 mL of alcohol because that alcohol would burn for quite awhile, but was not an excessive amount.
Trial One Calculations
Pressure (kPa): 100.65
Volume: 15.1 L
Moles: .48
R: 8.314
Temp: 290 K
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Mass of cold air: 13.92 g
Kilograms of air: .0132 kg
Weight of air: .136416
Mass of empty apparatus: .00856 kg
Weight of empty apparatus: .09163
Net force: .08388
Outside
Pressure (kPa): 100.65
Volume: 15.1 L
Moles: .43
R: 8.314
Temp: 318 K
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Mass of hot air: 10.75 g
Kilograms of air: .01075 kg
Weight of air: .10535
Mass of empty apparatus: x
Weight of empty apparatus: x
Net force: x
What happened?
We decided that we would try to lighten our basket, so it would have less weight to lift off the table. To do this, we made our basket much smaller (about 2 and a half inches in height, and two inches in diameter.) We kept all our other materials the same; we put three cotton balls with 5 mL of alcohol on them in the small basket and used the same pipe cleaners.
Trials Two and Three
Because of these, we needed to design a basket with more oxygen available to the fire. We cut our original tinfoil basket in half and poked a series of holes around the center to let more oxygen in. We took out one cotton ball and left everything else the same. When we tested the third balloon design, it didn't lift off again. The bag was leaning over instead of staying upright, so the heat coming off of the cotton balls wasn't centered under the basket. We also thought that our basket was still too heavy.

Trial Four!
We again used two cotton balls and 5 mL of alcohol spread evenly over them.
When we tested trial four, the bag filled up with hot air right away. As we'd hoped, the basket stayed centered under the bag, and the bag didn't lean in any direction. After awhile, the tinfoil basket started to hop, like our first trial, and eventually, it took off and went a ways into the air!
Trial Four Calculations
