Sometimes I am surprised when science hits me over the head during an everyday activity. I was at the Calgary Zoo a few weeks ago. One would expect that some biology may creep around the corner at you, but I didn’t really expect to see such an amazing example of refraction.
You can see the nose of the hippo clearly above the water. But when you look at the rest of the hippo beneath the surface it doesn’t even look like the nose belongs to the same individual.
The light waves that hit the camera from the nose of the hippo travelled through air, so they travelled faster than the waves from the rest of the body which had to travel through water. For a great (and short) video on why the speed of light is slower through different materials check out the Minute Physics video.
This is the same effect that makes it look like a straw bends as it enters a glass of water.
One of the best analogies for how this works is if you think of pushing a cart with four wheels. If you are pushing the cart along a hard floor all the wheels are travelling at the same speed. But, if one wheel hits a patch of carpet before the others do, that wheel will slow down relative to the rest. This will cause the cart to turn towards the slower wheel. When light moves from one medium to another at an angle other than 90˚, the side of the wave that hit the new medium first will change its velocity first causing the wave to bend. Once light moves from air into water, the light slows down. When it moves from water to air, it speeds up.
The result of all this science is one heck of a photo.