Light changes direction when transitioning from air to water due to the phenomenon of refraction, which occurs as photons interact with water atoms. This wave phenomenon can be understood by analyzing electromagnetic waves at the boundary between air and water. It is essential to reconsider traditional views of photons, as they do not behave like discrete particles but rather exhibit wave-like properties. Richard Feynman's book, "QED: The Strange Theory of Light and Matter," is recommended for a deeper understanding of photon behavior.
PREREQUISITESStudents of physics, optical engineers, and anyone interested in the fundamental principles of light behavior and quantum mechanics.
and get rid of the picture implied by your question: photons aren't like little bullets moving through space, and when a beam of light changes direction by reflection or refraction, it's not because a whole bunch of photons changed direction. Once you've forgotten everything you think you know about photons, you're ready to learn how they really behave, and for that I highly recommend Feynman's "QED: The strange theory of light and matter".