When a rod of metal is heated, compressive stress will be set up in the rod. The wire is not allowed to bend and the force is applied normal to it's cross sectional area.
Let 'L' be the length of wire, A be the area of cross section, Y be Young's modulus and '' be the coefficient of linear expansion, heated to a temperature ''.
If the rod was free then increase in length of wire due to rise in the temperature will be Lθ.
Here, since rod is not allowed to expand, therefore, compression in rod is equal to increase in the length of rod i.e. Lθ.
If S is the compression stress in rod then,
Hence stress is independent of the length of the wire.
Adhesive force is the attractive force between two unlike molecules. They are caused by forces acting between two substances like electrostatic force (attraction due to opposing charges), mechanical force etc.
E.g., Force of attraction between gum and paper.