Hello everyone, I am kind of new to this forum. If this post belongs elsewhere, please tell me, thanks. 1. What are mediators? Are they particles? Why does the four fundamental interactions each have one or more associated mediators? Moore (my textbook's author) writes: “Each interaction as one or more associated mediators that represent the interaction in quantum-mechanical calculations (what does this mean?). These calculations imagine a pair of particles interacting by exchanging mediators in a way that usually makes the mediators undetectable even in principle (I don’t understand this at all)” (11). So, the book also tells me that strong nuclear interaction associates with gluons (8 types); electromagnetic with photons; weak with vector bosons; and gravitational with graviton. 2. What are examples for each of the following contact interactions: friction interactions (which oppose the relative motion of the objects in contact); compression interactions (which seek to keep them from merging); and tension interactions (which oppose their separation) (Moore 13). The book gives no explanation as for how to identify these contact interactions. There are some examples, but I need a more complete definition or explanation or each so I am able to identify when these interactions occur. Thanks for everyone's help!