Light travels incredibly fast. In a vacuum, it speeds along at nearly six trillion miles per hour. Ever notice how your feet look distorted when you wade in the water, or how a straw seems to be cut in half where it enters a full glass? When light travels through a medium, it slows down. When a collection of light rays crosses from one material to another (from water into air, for instance), the change in speed warps the image.
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This warping effect can appear random, as in the case of rippling water, or it can be well-organized. We often take advantage of light’s transition between air and glass, for example, to bend images in a useful way. A magnifying glass works by taking a small image and spreading it out over a large area. What happens when you use it backwards– put a large cross-section of light in, then focus it down to a tiny point?
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Try this with the sun as a light source on a warm day, and you’ll find that the visible light and heat at the focus point are intense enough to burn wood!
Written By: Caela Barry

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