Normal stress is a critical part of structural design and analysis. It measures a material’s ability to withstand forces pushing or pulling directly on its surface (perpendicular to the surface). Think of it like this: normal stress determines whether a bridge can hold its weight or a building can stand tall without collapsing.
Understanding normal stress is essential in engineering and physics to prevent material failure. To help you calculate it, we’ve put together a normal stress calculator and tips for how to use it.
What is normal stress?
Normal stress is the amount of force acting perpendicular to a surface. To calculate it, you’ll need to know two things: the normal force and the area over which that force is distributed.
Normal force
Normal force is the force acting perpendicular to a surface, measured in Newtons.
Area
Area refers to the contact area over which the force is distributed, typically measured in square meters.
The formula
To calculate normal stress, you’ll use this formula:
Normal Stress = Normal Force / Area
or
NS = NF / A
How to calculate normal stress
Calculating normal stress is a straightforward process:
- First, find the normal force (NF).
- Then, find the total area (A) over which that force is applied.
- Next, use the formula: NS = NF / A, where NS stands for normal stress.
- Finally, calculate the normal stress.
For example, imagine that you have a force of 507 Newtons (N) applied over an area of 32 square meters (m2). Using the formula, the normal stress is 507 N / 32 m2, which equals 15.84 N/m2.
Normal stress is usually measured in Pascals (Pa) or Newtons per square meter (N/m2).
Tensile vs. Compressive Stress
Normal stress can be either tensile or compressive, depending on the direction of the force.
Tensile Stress
Tensile stress is a pulling or stretching force. If you imagine trying to pull something apart, you’re applying tensile stress.
Tensile stress is considered negative normal stress and indicates that a material is being stretched.
Compressive Stress
Compressive stress is a pushing or compressing force. Think about squeezing an object between your hands; that’s compressive stress.
Stress on a pillar is compressive (negative) because of the weight pressing down from above.
Normal stress and material properties
Materials react to normal stress in different ways, depending on their properties. Here’s a quick look at how materials behave under stress:
Elastic deformation
When a material deforms elastically, it’s a temporary change. The material goes back to its original shape once the stress is removed. Young’s modulus measures a material’s stiffness, that is, its resistance to elastic deformation.
Plastic deformation
Plastic deformation is a permanent change. Once a material is stressed past its yield strength, it’ll stay changed. Yield strength is the maximum stress the material can take before it’s permanently deformed.
Failure
If normal stress is too high, the material will fail, either by fracturing or by deforming so much that it can no longer function. Ultimate tensile strength is the maximum stress a material can withstand before it fails.
Summary
Normal stress is the measure of force acting perpendicularly on a surface area. To calculate it, you divide the normal force by the area of contact.
A solid understanding of normal stress is essential for structural design and analysis in engineering and architecture.
If you’d like to learn more about how forces affect materials, you can explore related topics like shear stress and material behavior.