# Friction versus Shear

• Post by:
• August 21, 2021

Friction and shear stress are two phenomena involved in the field of mechanics of matter. It is very important to have a good understanding of both friction and shear stress in order to get a good understanding of fields such as screenprinting, electrical engineering, automobile engineering, mechanical engineering, and any other relevant field. Both friction and shear stress plays important roles in our day-to-day lives too. If it is not for these forces, we would not be able to do most of our daily work.

### Friction

Friction is probably the most common resistive force we experience every day. Friction is caused by the contact between two rough surfaces. Friction has five modes. Dry friction, which occurs between two solid bodies, fluid friction, which is also known as viscosity, lubricated friction, where two solids are separated by a liquid layer, skin friction, which opposes a moving solid in a liquid, and internal friction, which causes the internal components of a solid to make friction.

However, the term “friction” is most commonly used in place of dry friction. This is caused by the rough microscopic cavities on each of the surfaces fitting each other and refusing to move. The dry friction between two surfaces depends on the friction coefficient and the reactive force normal to the plane acting on the object. The maximum static friction between two surfaces is just a bit higher than the dynamic friction. It should be noted that even though friction depends on the normal reactive force, it is always tangential to the surface, thereby, normal to the reactive force.

### Shear Stress

Shear stress is a deformation force. When a force is applied tangentially to a solid surface the solid tends to “twist”. For this to happen, the solid must be fixed, so that, it cannot move in the direction of the force. The unit of shear stress is Newton per meter squared or commonly known as Pascal. We know that Pascal is also the unit of pressure.

But, the definition of pressure is the force normal to the surface divided by the area, whereas the definition of shear stress is the force parallel to the surface per unit area. Torque acting upon a fixed object can also produce shear stress. By definition, not only solids but also fluids can have shear stress. Objects have a property called the shear modulus, which tells us how far will the object twist for given shear stress. This depends on the shape, size, material, and temperature of the object. Shear stress of constructions and automobile engineering plays the main role in designing and implementing the design.

### Summary

• Friction can be a cause of shear stress.
• Friction is measured in Newton, while the shear stress is measured in Pascal.
• Friction is a force, while the shear stress is a force per unit area.
• Friction depends on both of the contact surfaces, while shear stress depends only on the force parallel to the surface per unit area.

DID YOU FIND THIS INFORMATION USEFUL?