Rise and Fall
Cooper Barrow
Award: Top 100
School: kentucky country day school
Teacher: lillian apple
Category: Contrived
Photo #20837
Rise and Fall
When you imagine physical heat and cold, you can hardly envision them in your head. But when light is manipulated in just the right way, hot and cold can be brought to life, displaying a vibrant dance as they rise and fall. The photo shows the convection of dense, cold carbon dioxide gas and the sparse, swirling heat of a candle flame, circulating in opposing directions. This visual phenomenon is only possible through Schlieren photography.
Schlieren photography works by taking advantage of something most people never think about. Light does not travel at exactly the same speed through all air. When air changes temperature or density, its refractive index changes too, and that causes light rays to bend slightly off course. Normally, you would never notice. Schlieren photography makes those tiny bends visible.
The setup focuses a beam of light onto a sharp edge positioned at the mirror's focal point. Any air disturbance between the light source and the mirror deflects rays toward or away from that edge, creating the bright and dark regions visible in the photo. What looks like smoke or flame in the image is actually the bending of light itself. You are not seeing the gas; you are seeing its effect on the light passing through it.
The candle flame heats the surrounding air, reducing its density and causing it to rise through thermal buoyancy. The dry ice sublimates into carbon dioxide gas, which, at a molecular weight of 44 grams per mole, is significantly denser than ordinary air. Gravity pulls it downward. The luminous white boundary in the center marks the turbulent mixing zone where the two opposing flows collide. Cellophane gels over the light sources enhance the visual contrast between the two flows, making the otherwise invisible forces distinguishable.
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