Applying simple shear to two plates | pressku.com

I publication that nan exertion of shear requires that adjacent and other forces are applied to 2 parallel plates. Why is this nan case? If nan unit connected 1 sheet is transmitted done nan worldly to nan bottommost surface, and nan bottommost aboveground is held truthful that it doesn't move by applying a unit successful nan other guidance from nan unit connected nan apical plate, wouldn't that unit besides beryllium knowledgeable by nan apical plate, truthful that successful some cases you aren't experiencing a nett force? How do you clasp nan bottommost sheet truthful that it doesn't move?