Floating Tea BagsMarcus SpataroAward: Top 100
School: sleepy hollow high school I got the photo idea from a demonstration we did in class at the start of the year. This demonstration taught us about convection: how fluids like air transfer thermal energy. The first phenomenon that occurs in the photo is combustion, the chemical reaction that occurs after lighting the tea bags, when they begin releasing heat, ash, and hot gas. This is the trigger for all following principles. Since the air has been heated, the molecules move faster and they collide harder thus creating greater pressure. This is described by the ideal gas law. The hot air then expands into lower pressure cold air, creating a buoyancy force because it is now less dense. This force, along with gravity and drag, all have an effect on its upward motion. I observed that after lighting the bags, it took a couple of seconds before lift off, and then they quickly accelerated upwards. This was due to the bags having a greater mass and therefore a greater force of gravity acting on them. After some of the mass was reduced via combustion, the buoyancy force ended up greater than the weight, causing them to accelerate upwards, which is why we say hot air rises due to convection currents. I observed this when the bags had turned fully to ash, but kept moving upward. This is similar to birds riding a thermal, allowing them to move up or stay aloft for longer without having to expend energy by flapping their wings. 
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