The blades of scissors are opposing forces that clash, and collide in a sense, but if they actually impact one another they jam and are obviously working wrong. They have a still point of connection where one is fixed and the other in rotation -- and a moving point of connection that advances on a line. Their action is soft, connected, meshing, blended and they do not harm one another at all, --- but they destroy anything that comes between them.
As a physical interaction they describe perfectly what NOT to do to make aiki. On contact; it's tenkan or irimi, not aiki.