What kind of geometry is used when objects in water stick out and form an illusion?

Kasia: What kind of geometry is used when objects in water stick out and form an illusion?
Sorry my question might sound a little confusing…
but what i mean is, say you have a reed in a pond. The part of the reed that sticks out above water looks straight, but the part that is underwater looks diagonal. A lot of straight things make this illusion when you put them in water, even a straw in a cup of soda.
What is this illusion called? and does it use any geometry?

Answers and Views:

Answer by Ms. Worth
The phenomenon is called “refraction.”

https://en.wikipedia.org/wiki/Refraction

Answer by mslinda8393
I believe it is called refraction. The light in the water refracts the object and makes it look bent. I don’t know about the use of geometry here.

Answer by Haley
Refraction. Remember, fraction is broke or bent so the “re”fraction, is the same! ( :