The process of parallel layers sliding past each other is known as shearing. A pile of papers, a pack of cards with rectangular cross-section can be pushed to obtain a parallelogram cross-section. In such cases, the angle between the sides has changed, but all that has actually happened is some parallel sliding. In this article, let us discuss shearing stress in detail.
Shearing Stress – What Does It Mean?
When an external force acts on an object, It undergoes deformation. If the direction of the force is parallel to the plane of the object. The deformation will be along that plane. The stress experienced by the object here is shear stress or tangential stress.
It arises when the force vector components which are parallel to the cross-sectional area of the material. In the case of normal/longitudinal stress, The force vectors will be perpendicular to the cross-sectional area on which it acts.
Shearing Stress is defined as:
“A type of stress that acts coplanar with cross section of material.”
Shear stress arises due to shear forces. They are the pair of forces acting on opposite sides of a body with the same magnitude and opposite direction. Shear stress is a vector quantity. Which means, here the direction is also involved along with magnitude. It is denoted by the Greek alphabet: \(\tau\). The SI unit of shear stress is N/m2 or Pa
How is Shearing Stress Calculated?
Average shear stress can be calculated by taking the ratio of force per unit area
- \(\tau\) is the shear stress
- F is the force applied.
- A is the area of cross-section, that is parallel to the force vector.
Shearing Stress in Fluids
Shear stress is observed in fluids too. When a fluid flows within the boundary of solids, the shear stress is observed along with the point of contact between fluid and boundary. Fluid comprises of various levels, each level travel at different speeds. The layers which are at the same height from the boundary experience same speed. This varying speed between the layers is also a result of shear stress. In fluids, stress and strain are related differently. Here, shear stress is proportional to strain rate with viscosity as proportionality constant.
Shearing Strain in Real Life
The moment you wake up and crawl on the bed to get out of the bed, till you go back to sleep. Almost every instance of the day to day activity involve shear stress. Some of such real-life scenario are listed below-
- All forms of cutting (Cutting fruits, vegetables, paper, cloth, tree etc)
- Painting, Brushing, Applying creams/soaps/lotion/ointment etc.
- While Chewing food between the teeth’s.
- While walking or running while our feet push ground back to move forward.
- When a moving vehicle starts or stops, The surface of the seat experience the shear stress.
- When water flows River beds experience shear stress. Sometimes as a result of this erosion can be noticed.
- On the smartphone screens while sliding.
- While preparing Indian bread like Dosa, Roti, Pizza base etc.
- Polishing the surface.
- Writing on blackboard with chalk piece
- On sliding etc.
If we start to list out, the list will run for pages. To brief, Shear stress is an unavoidable event involved in our day to day life.
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