1. The problem statement, all variables and given/known data Was performing the online "reading questions" for my Physics 2 course. And I came to this question. "A wave is not a material thing but a disturbance moving through a medium. The way that it propagates is that every part of the medium it encounters begins to vibrate in time with the wave and therefore with the original cause of the disturbance. Each part of the medium which is set to vibrating thereby becomes a new source of the wave and new waves radiate outwards from it in all directions. This idea is known as:" Now after reading through the chapter a few times, Ive not been able to see the mention of any laws, or statements that really seem to match this. Any idea on where I may find such information? 2. Relevant equations Possible choices in this case. Newton's conjecture Einstein's hypothesis Hyghen's principle Maxwell's proposal Faraday's paradox 3. The attempt at a solution If I recall correctly. Einsteins hypothesis referred to the idea of the moving of electric, and magnetic fields in parralel. While Faraday's Paradox has to do with magnetism. I'm thinking it may be Hyghen's principle as it refers to the idea of light radiating in all directions. But at least as read, it doesn't make any mention about the part which might refer to the idea of the object vibrating in synch and thus appearing to become the source of the waves being emitted. Can I get some help with this, or at least be pointed in the right direction? Thanks!