The Hot Air Balloon Challenge

By Emily and Michael

Materials

For our first, second, and third balloon trials, we used:

-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

Our original design consisted of a medium size tinfoil basket (that we shaped using a 250 mL beaker), connected with two pipe cleaners (one on either side of the basket) to our eight gallon bag (we poked them in the side.) We felt that the pipe cleaners would do a good job of holding up the basket (the weight was evenly distributed between the pipe cleaners), and the tinfoil basket was a good size; it allowed in enough oxygen to produce good heat.



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

Inside

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?

Trial One almost worked. The plastic bag filled with air, and our basket hopped around but never fully got off of the ground. Our pipe cleaners worked well to hold up the basket, they were a good length away from the balloon basket, and our balloon didn't melt or anything of that sort. The three cotton balls with alcohol provided a good amount of heat, and that heat reached the balloon. Unfortunately, it just didn't quite get off the table.


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

Our second test was highly unsuccessful. This time, the balloon filled up with air, as it should've, but the basket didn't show any sign of leaving the table. The flame was extremely little, and we concluded that there wasn't enough oxygen getting to the fire. Our cotton balls were extremely close together and having three of them stuffed in there was reducing the oxygen and making the basket heavier than necessary.


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.

The paper design for trial four!

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Trial Four!

For our last trial, we completely redid our design. Instead of using a cup-type basket, we used a flat piece of tinfoil with half-inch walls on all four sides. It was a much lighter basket. We also used four pieces of wire, each about eight inches long. We attached the wire to our bag and basket by poking holes and twisting it. Having an anchor on every side of the bag and basket meant that the basket would stay centered and steady underneath the bag.

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

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Why did the balloon fly?

The lighted cotton balls produced heat, and the heat filled up the volume of the air balloon. As the balloon heated up, so did the pressure inside of the balloon, because as we learned in this unit, when heat increases, the pressure increases. The molecules in the balloon began escaping out of the bottom, and as they left, the density of the balloon went down, thus making the balloon less dense than the air around it. This caused the balloon to float.