# Concept of Stress: Why stress is needed?

• koolraj09
In summary, the concept of stress evolved as a way to describe the internal forces acting within a deformable body. It is defined as force per unit area and is useful in determining the strength and behavior of different materials. While it may seem hypothetical because it cannot be directly measured, it is a vital concept in engineering and physics.

#### koolraj09

Hi guys. Just out of curiosity I want to know that why the concept of stress evolved? Why do we need stress?

Why do we need stress?

To make lazy students work and explain what they mean?

Why is it that stress has to be defined the way it is...i.e internal restoring force per unit area?? Why did the researchers put it that way? I'm interested is in the physical significance of stress(since stress is a hypothetical quantity).

<time travel back 30 years to my Advanced Machine Design class in graduate school...bzzzzzt! >

I vaguely recall that the concept of stress was developed to describe a field of force applied to particle: dF/dA. It integrated to F/A. It was a useful concept because it allowed one to derive high-order equations that provided a uniform description of how force was applied to objects.

Hope this helps. Like I said, it was long time ago. I also learned that most of the equations used by engineers in common practice are chock-full of estimations that eliminate the higher-order equation components. What's a few percent of error between friends anyway?

<back to future/present day...bzzzzt! :tongue: >

I'm not sure why you call stress a hypothetical quantity. It's no more hypothetical than pressure (and the units are the same, of course).

Stress is useful for describing how different materials behave, in a way that is independent of the shape of particular objects made form the materials. For example Young's modulus (stress / strain ) describes how rigid or "stretchy" different materials are. If the stress is higher than the elastic limit for a material, it will not return to its original shape when you remove the loads that caused the stress. If the stress is higher than the "ultimate stress", the material will crack or break.

As a simple example, the force needed to break a piece of wire depends on the material it is made from, and also on the thickness of the wire, but the stress needed to break it only depends on the material. The same stress level will also break a cantilever beam, or a plate, or anything else made from the same material.

From Wikipedia:
stress is a measure of the internal forces acting within a deformable body.

Instead of looking at it as force per unit area, look at it as force per molecule. Stress is useful to determine how strong a material is. When a part breaks under a certain force, we actually break the molecular bonds between the particles. The greater the area of the fracture, the higher the number of molecules, the greater the force needed.

I like to think of stress as way of comparing how different geometries and materials act under the applied load. This let's me decide on the best geometry and type of material to use for the intended application.

Hi AlephZero...
I think stress as a hypothetical quantity because we can't see or directly measure it!
On the other hand we can see/measure strain.

koolraj09 said:
Hi AlephZero...
I think stress as a hypothetical quantity because we can't see or directly measure it!
On the other hand we can see/measure strain.

How does that make it hypothetical? Considering the definition of the word, it doesn't make any sense to me.

You might not see the affects of the load on the material, but you can see what's applying a force to it and the material itself. What about Reynolds number and the lift coefficient, do you think they're hypothetical too?

What my experience says is Stress is the resistant provided by the material. Hence the name. It something like the stress/tension that is present in our body/mind too. Just because you can't see or measure it does it mean its not present. I just gave a rough analogy here.
Hope this helped :) :shy:

@koolraj

You said stress = force/area..
What force? what area?

When you first start considering internal forces within a body it is tempting to try to continue to work in force terms only , as you did with forces between bodies.

However try to explain why an auto tyre (which is round off the vehicle) has the shape it does and describe what forces are acting and over what areas in terms of forces.

Then you will see the need for the stress concept.

## 1. What is stress?

Stress is a physiological and psychological response to a perceived threat or demand. It is a natural reaction that helps us adapt and cope with challenging situations.

## 2. Why do we need stress?

Stress is necessary for our survival and success. It motivates us to take action and overcome obstacles. It also helps us to develop resilience and problem-solving skills.

## 3. How does stress affect the body?

Stress triggers the release of hormones, such as adrenaline and cortisol, which prepare the body for a fight or flight response. This can lead to physical symptoms such as increased heart rate, muscle tension, and shallow breathing. Chronic stress can also have negative effects on the immune, digestive, and cardiovascular systems.

## 4. What are the different types of stress?

There are three main types of stress: acute stress, episodic acute stress, and chronic stress. Acute stress is short-term and can be caused by a specific event or situation. Episodic acute stress is when someone experiences frequent acute stress episodes. Chronic stress is long-term and can be caused by ongoing challenges or traumatic events.

## 5. How can we manage stress?

There are various ways to manage stress, including exercise, relaxation techniques, healthy coping mechanisms, and seeking support from friends, family, or a mental health professional. It is important to identify the source of stress and develop a plan to address it effectively. Self-care practices, such as maintaining a balanced diet and getting enough sleep, can also help to reduce stress levels.