eli5, what is a knot in a plank of wood (or tree) and why are they so much harder to cut through?

Question

eli5, what is a knot in a plank of wood (or tree) and why are they so much harder to cut through?

In: Earth Science

Answer 1

IIRC a knot is the base of a branch or bough splitting off from the tree itself. It’s harder than the surroundong wood because the grain is perpendicular to the grain of the surrounding wood.