Optics
Eyeglasses, contact lenses, microscopes, movie projectors, cameras, and more all exist because of the physics of light, or optics. These innovations harness the principle of refraction or the angle at which light bends when entering a different material.
For example, glass lenses—similar to the lens of an eye—use refraction to focus and magnify images. Refraction also creates the strange image of a disproportionately squat lower half when a person stands waist-deep in a pool.
Light travels slower in water, so the human eye gazing at the pool from above perceives objects in water as closer than they actually are.
