When 2 waves interefere (or collide with eachother), it usually affects the crest of the wave. If both waves collide with both crests, it will create an amplified crest, and the waves will pass through eachother afterwards. If a trough of a wave meets a crest, it will cause the crest to be lowered shortly before both continue on.
I believe they are called Rhizomes.
Answer:
Keepers also have a useful safety function, as they stop external metal being attracted to the magnet. ... A keeper for low-coercivity magnets is just a strong permanent magnet that keeps all the domains pointing the same way and realigns those that may have gone astray.
