When shooting a fish in water with a slingshot, where should I aim at the fish?

The position where the fish is deflected downward, according to the principle of water refraction.

When light is projected obliquely from one transparent medium (e.g., air) into another (e.g., water), the direction of propagation generally changes, a phenomenon called refraction of light.

Refraction, also known as refraction, is an optical term that refers to the phenomenon in which the direction of light travels changes due to the difference in wave speeds when light enters from one medium into another, or when it travels through parts of the same medium with different refractive indices.

For example, when a stick is inserted into water, the naked eye alone will think that the stick is bent when it enters the water, which is the refraction of light when it enters the water to bring about this effect.

Light from the dense (that is, light in which the speed of propagation is small) medium to the sparse (that is, light in which the speed of propagation is large) medium of the interface, all be reflected back to the original medium of the phenomenon.

When light is directed to the interface of the two media, only the phenomenon of reflection without refraction. When light from a light-dense medium to light-sparse medium, the angle of refraction will be greater than the angle of incidence.

When the angle of incidence increases to a certain value, the angle of refraction will reach 90 °, then in the light sparse medium will not appear in the refracted light, as long as the angle of incidence is greater than the above values, are no longer exist in the phenomenon of refraction, which is total reflection. So the conditions for total reflection are: ① light must be from the light dense medium to light sparse medium. ② angle of incidence must be greater than the critical angle.

The critical angle is the refractive angle of 90 degrees corresponding to the angle of incidence (only light from the light-dense medium into the light-sparse medium and the angle of incidence is greater than the critical angle, total reflection occurs)