Can someone explain to me if a domino is a lever and why?

depends in how it is used. if the domino is perched on a point where it is balance and each end is hanging, then it is a lever. i would not consider a domino that is standing and is pushed to start a chain reaction a lever. if it were on the edge of a table and then it was hit with something to be flicked across the room, then it would be a lever.