The intensity of resisting force normal to the sectional plane is called as:
Intensity of normal stress
In the field of mechanics of materials, when an external force is applied to a body, the material within the body develops internal forces to resist this external loading. These internal forces are distributed over the cross-sectional area of the material.
Normal Stress Concept
The question defines a very specific aspect of these internal forces: "the intensity of resisting force normal to the sectional plane". Let's break down what each part means:
- Resisting Force: These are the internal forces developed within the material to oppose external loads.
- Normal to the Sectional Plane: This specifies the direction of the resisting force. "Normal" means perpendicular or at a 90-degree angle to the cross-sectional area of the material. This is distinct from forces acting parallel to the surface, which lead to shear stress.
- Intensity: This term refers to the force distributed over a unit area. In mechanics, intensity is typically expressed as force per unit area.
Combining these elements, the concept described is precisely normal stress.
Defining Normal Stress
Normal stress (\(\sigma\)) is formally defined as the internal resisting force acting perpendicular to a unit cross-sectional area. It is a fundamental measure of how internal forces are distributed within a deformable body. The mathematical representation for normal stress is:
\(\sigma = \frac{F_n}{A}\)
Where:
- \(F_n\) represents the component of the internal resisting force that acts normal (perpendicular) to the cross-sectional area.
- \(A\) represents the cross-sectional area over which this normal force is distributed.
Normal stress can be either tensile (pulling apart) or compressive (pushing together), depending on the direction of the resisting force.
Analysis of Given Options
| Option | Explanation |
|---|---|
| Intensity of Compression | Compression is a specific type of normal stress where the material is subjected to forces that push it together, causing it to shorten. While it involves resisting forces normal to the plane, it is a sub-category of normal stress, not the overarching term for any such force. |
| Intensity of Tension | Tension is another specific type of normal stress where the material is subjected to forces that pull it apart, causing it to elongate. Like compression, it is a specific manifestation of normal stress, not the general definition. |
| Intensity of normal stress | This option perfectly matches the definition provided in the question. It encompasses any resisting force acting perpendicular to the sectional plane, whether it causes tension or compression. It correctly identifies the intensity (force per unit area) of the normal component of the internal resisting force. |
| Strain | Strain is a measure of deformation, not force intensity. It quantifies the amount of deformation (change in dimension) relative to the original dimension of a material when subjected to stress. Strain is typically dimensionless or expressed as a ratio (e.g., mm/mm) and is fundamentally different from stress. |
Distinguishing Stress from Strain
It is important to remember the key difference between stress and strain in mechanics of materials:
- Stress describes the internal resisting forces per unit area within a material.
- Strain describes the material's deformation or change in shape due to these internal forces.
Conclusion on Resisting Force
Therefore, the term that accurately describes the "intensity of resisting force normal to the sectional plane" is the intensity of normal stress. This concept is fundamental for understanding the mechanical behavior and strength of materials under various loading conditions.
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