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Mechanical Properties of Solids

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Physics Part II

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Class 10 Class 12
A rod of metal is clamped between two rigid supports and is heated by temperature θ. If wire is not allowed to bend then what type of stress will be set up in the wire and how does stress developed in wire depend on length of the wire? 

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 'α' be the coefficient of linear expansion, heated to a temperature 'θ'.
If the rod was free then increase in length of wire due to rise in the temperature will be Lαθ.

Here, since rod is not allowed to expand, therefore, compression in rod is equal to increase in the length of rod i.e. Lαθ. 

If S is the compression stress in rod then,

Y = SLLαθ=Sαθor     S=Yαθ

Hence stress is independent of the length of the wire.


What is the force of adhesion?

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.


What do you understand by intermolecular forces?

Intermolecular force is the force between the molecules of the substance is called intermolecular force.

There is a dipole-dipole interaction between the molecules.

Define interatomic forces and give an example?

The force between atoms of the molecule is called interatomic force.

E.g.The nucleus and electron cloud of a molecule is binded by electrostatic force. 

What is the force of cohesion?

Cohesive attraction or cohesive force is the force of attraction between same types of molecules sticking together. 

What is the nature of inter-atomic or inter-molecular forces?

Inter-atomic or inter-molecular forces are electrostatic in nature.