Science Buddies: "Ask an Expert"

I need help regarding one of your posted science experiments.
My daughter and I just completed your "Up Up and Away in Your Own Hot-air Balloon" experiment
https://www.sciencebuddies.org/science- ... p041.shtml
and got very mixed results. The idea was to see if the size of the balloon effected it's flight. We timed the flight of 4 different balloons, and flew each balloon 3 times.

We are not sure what to do with the results; as the size of the bag changed, the results we got were very random. They did not stay the same, go up consistently, or go down consistently. Please help! Are there any published results of this experiment so we can see what was supposed to happen? We just spent all day on this and have no time or materials to re-do the experiment.

lindarm - I've never done this experiment, but it seems that the larger the bag, the more rapid the ascent, (once you released it) the longer it would stay aloft, and the slower it would descend. That's just my intuition. There are several variables that can confuse your results. Consistency in the temperature of the air in the bag is important. If you used the toaster as a source, it would take longer to fill the largest bag with hot air. Did you let rising warm air force out the the majority of cooler air inside the bag to the point that you achieved a pretty warm air temperature in the bag? That might mean that you would have to leave the bag over the toaster for a longer time when it was in its largest form. Did warm air spill out while it was aloft? It seems important that the 'post-it' notes needed to stabilize the skirt of the bag. If the bag became unstable from the vertical, you could lose warm air and greatly reduce the performance of the bag.

I don't know what you can do except re-run the experiment attempting to control some of these variables very closely. Your results should not be 'random'. Good luck, hope this helps.

Rick Marz