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2009 High School Physics Photo Contest

Winner's Showcase

 

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Honorable Mention - Natural

Title: Falling Liquids Tend to Form Spherical Drops
Student: Austin Thomas Ferro
School: Mission College Preparatory, San Luis Obispo, California
Teacher: Vickie Backman

There exists a misconception that falling droplets of water are tear shaped, similar to a drop hanging from a faucet. This is not the case. When a liquid such as water free falls, the surface tension of the droplet causes the molecules to arrange themselves in such a way as to minimize the surface area of the droplet relative to its volume. The attraction between molecules on the surface of the drop is greater than between those within the drop because the surface molecules have no neighboring atoms outside of the drop with which to interact; they therefore experience increased attraction towards each other, relative to the molecules inside the droplet. For this reason, water falling in air tends to form a sphere, the shape that minimizes the surface area relative to volume for any given droplet. When water droplets exceed 1-2 millimeter in size, the effect of the pressure of air resisting the bottom of the falling drop causes them to flatten out. This has been described as a ?hamburger bun? shape. Larger drops fall faster and experience more air resistance on their bottom surfaces, causing them to form ring-structures that break apart into smaller droplets. This picture demonstrates the elongation of droplets as they leave a faucet. This is a result of surface tension. Once the droplets separate from the stream of water, they assume a spherical shape, minimizing their surface area relative to their volume.

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