Define stress. How does an object behave in between the elastic and plastic region when it is given a tensile stress from it’s sides?

Stress, in terms of physics and engineering, is defined as the force per unit area within materials that arises from externally applied forces, uneven heating, or permanent deformation. It is denoted by the Greek letter 'σ'. It directly influences the strain or deformation of an object.

When an object is subjected to tensile stress from its sides, it behaves differently in the elastic and plastic regions.

1. Elastic Region: In this region, the object returns to its original shape and size once the stress is removed. This is due to the temporary deformation. The relationship between stress and strain in this region is given by Hooke's Law, which states that the strain in a solid is proportional to the applied stress within the elastic limit of that solid.

2. Plastic Region: If the stress increases beyond the elastic limit, the object enters the plastic region. In this region, the object will not return to its original shape or size even after the stress is removed. This is due to the permanent deformation.

Between the elastic and plastic region, there is a point known as the yield point. At the yield point, the object starts to deform plastically. If the stress is removed at any point in this region, the object will have a permanent deformation. The object behaves elastically before the yield point and plastically after the yield point.