# Direct Shear Force

In a previous article we discussed the definition of a force and discussed how a normal force acts perpendicular to an area to produce a normal stress. However, there is another main type of force in addition to a normal force, this is a shear force.

A shear force is a force that is applied parallel to a plane, not perpendicular to it. Instead of trying to extend or squash an element like a normal force, a shear force tries to deform an element sideways.

A shear force is simply a force acting in a specific direction, i.e. parallel to a plane. The units of shear force are therefore the same as the units of normal force, newtons, N. Typically structural engineers analyses shear forces that are typically in the order of magnitude of kilonewtons, kN

As with a normal force, any applied force also needs to have a reaction, again this takes the form of an equal and opposite force. Figure 2: A shear force must satisfy force equilibrium, a shear force reaction resists an applied shear force.

As with force equilibrium, shear forces applied to an element or a system need to be in equilibrium, if not an acceleration occurs. In a beam, when a load is applied vertically, it generates a shear force in the cross section of the element. In the example below the applied load generates a shear force, shear force equilibrium is provided by the resulting reaction at the beam end.