Download Stress Definition for a Layman

William Mak
Stress Definition for a Layman
Stress is defined as the force over the area of an object. Force is related to the
amount of pressure applied to an object (The American Heritage, 2006). The word stress
comes from the shortening of the middle French word “destresse” to mean hardship,
adversity, force, and pressure and the Middle English word stresse (The American
Heritage, 2006). Stress exerted over a specified area can lead to strain. Strain occurs
when stress causes relative deformation in a material. The level of stress on an object is
dependant on two variables: (1) the direction and magnitude of the force (2) the
composition and shape of the material.
The direction of the force is directly related to stress because force can be applied
either perpendicular to the surface of the object or parallel to it; both would cause strain
on the object to change. Force that is applied perpendicular to the surface of an object
causes normal stress and is the most common form of stress. It can lead to bending and
twisting depending on where the force is being applied. Bending occurs when a
perpendicular force is applied along one axis of the surface. Twisting occurs when
perpendicular forces are applied at two different axes of the surface. Force being applied
parallel to an object can be split up into two different types of stress (1) Shear stress and
(2) Tensile stress (Hallidy, Resnick, Walker, 2005). Force applied parallel to the object
along one direction would be called shear stress and if the shear stress on a material
becomes too great it would lead to shearing. Shearing occurs when the object deforms
along the direction of the force. Tensile stress is when forces are acting away from each
other on both ends of an object, such as a rod. This would lead to stretching in the object.
When the forces are acting towards each other then it would be called compressive stress
and can lead to compression. Shearing, bending, twisting, stretching, and compression are
all examples of strain (Encyclopedia Britannica, 2006). Stress on a material does not
mean it must cause these results, but can lead to any of the outcomes if there is a lot of
stress.
The level of stress also depends on the composition and shape of the material. For
instance, metal can withstand more stress than wood. Different materials have varying
levels of stress capacity (Encyclopedia Britannica, 2006). Furthermore, depending on the
shape of the material, it can result in different effects when stress is applied to it. For
example, a piece of paper fashioned into a cylinder has a higher resistance to compressive
strength than a piece of paper fashioned into a hollow rectangular cube.
Visual examples of stress can be seen in fig. 1 on the next page.
Therefore, stress is dependant on the direction of force and the composition &
shape of the material. To sum up, force that is applied parallel to the area of a surface
would cause shearing, stretching, and compression, while normal stress is force applied
perpendicular to the area of the surface which can cause bending and twisting.
Fig 1. Shows examples of each stress-induced reaction in physics and shows the forces
acting on the object that causes stress represented by the thin arrows.
One application of stress in physics is the law of elasticity discovered by Robert Hooke in
1660, which states that, the force (stress) being applied to an object is proportional to the
deformation (strain) on the object (Hallidy, Resnick, Walker, 2005). This law allows us
to understand what is happening when an object with elastic properties, such as a spring,
is being compressed as shown in Fig. 1.