The word ‘shear’ means to remove a part of a body by cutting or clipping it. Hence, a force applied to a structure that tends to shear or split it into sections is known as the shear force. It is applied in a direction perpendicular to the surface. One part of the structure is pushed in one direction, whereas the other part is pushed in the opposite direction. The shear force applied on a point divides the structure into two sections. If the section present to the left of the point of contact is pushed in the upward direction, and the right section is pushed downwards, the shear force is considered to be positive. However, it is considered negative if the left section is pushed in the downward direction, while the section present to the right is pushed upward. It is defined as the algebraic sum of the forces acting on the left-hand side or right-hand side of the section. Shear force is measured in Newtons.
Examples of Shear Force
A pair of scissors is a classic example to demonstrate shear force. When an object, for example, a piece of paper is placed between the two metal blades of a pair of scissors, it gets divided into two parts only because of the shear force.
2. Cutting a Piece of Wood
To cut a piece of wood, an axe or a saw tooth blade is held parallel to the object. The blade is kept in close contact with the wood. The mechanical force applied by the person to the blade gets transferred to the piece of wood. This force cuts the wood piece apart into two pieces. Hence, a shear force is said to be present.
3. Slicing a Bread
While slicing bread, a knife is held perpendicular to the loaf. When a force is exerted on the knife, it gets suspended into the structure. Due to the smaller surface area of the knife, the bread gets cut into two sections. Both the sections are pushed in opposite directions. The perpendicular nature of the force and the sections being pushed in the opposite directions indicate the presence of a shear force.
4. Cutting Vegetables
One of the greatest applications of shear force can be seen in cutting vegetables or fruits. To chop vegetables or fruits, a knife is held in a parallel direction, and the force is transferred to the object through the knife. The force acting on the object shears or splits it into two sections. One section of the vegetable receives an upward push, whereas the other section gets pushed downwards.
5. Trimming Hair
While trimming or cutting hair using a trimmer or a scissor, a force is applied to detach a portion of hair. The force is applied in such a way that it does not stretch the hair because it will cause tension. The trimmer or the scissor is held parallel to the hair. The shear force clips and separates the section of hair present on either side of the blade from each other. Both the sections are then pushed in opposite directions.
6. Nail cutter
A nail cutter detaches the unwanted length of the nail. When the sharp edges of a nail cutter are pressed against the nails, we get rid of the unwanted growth of nails, and this is possible only because of the shear force.
7. Chewing Food
The force applied by the teeth on the food acts in a perpendicular direction. This helps the food to get divided into smaller sections after every chew. The repeated chew or repeated application of a shear force makes the food particles small and the swallowing process easy.
While walking in a particular direction, both the feet apply force in opposite directions. One foot exerts pressure on the ground in a forwarding direction, whereas the other foot applies force in the backward direction. The force applied to the opposite sections exists in a perpendicular direction. Hence, a shear force is said to be present.