Definition of Fluid: What is Shear Stress?

In summary, the conversation discusses the definition of a fluid as a substance that deforms under an applied shear stress and includes both liquids and gases. The use of tangential force in the definition is due to the fact that fluids can also deform under their own weight. The compressibility of fluids is not included in the definition, as even in compressible fluids, only shear stress can cause flow.
  • #1
Micko
43
0
Hello,
I have found the following definition in wikipedia:
A fluid is defined as a substance that continually deforms (flows) under an applied shear stress. All liquids and all gases are fluids.
However, it's pretty hard for me to understand this definition. Shear stress represents tangential pressure applied. Fluid will also deform under perpendicular force. Why tangential force is used in definition?

Thanks
 
Physics news on Phys.org
  • #2
A fluid will deform by it's own weight, which can be tangential to the surface holding the fluid.
Not sure if that answers your question though.
 
  • #3
Micko said:
Fluid will also deform under perpendicular force. Why tangential force is used in definition?
Gasses will deform under perpendicular force, ie they are compressible. Liquids do not. Fluids include both liquids and gasses, so compressibility cannot be part of the definition.

Also, even in a compressible fluid, the "perpendicular" deformation is not continuous. So a normal stress does not cause a fluid to flow, only a shear stress.
 

Related to Definition of Fluid: What is Shear Stress?

1. What is the definition of fluid?

A fluid is a substance that can flow and take the shape of its container. It includes both liquids and gases.

2. How is shear stress defined?

Shear stress is a type of stress that occurs when forces are applied parallel to each other but in opposite directions. It is measured as the amount of force per unit area that is required to cause the deformation of a fluid.

3. What factors affect shear stress in fluids?

The viscosity, or thickness, of the fluid and the rate at which it is being deformed both affect the amount of shear stress that a fluid will experience. Other factors such as temperature and pressure can also impact shear stress.

4. What are some examples of shear stress in everyday life?

Shear stress can be seen in many everyday situations, such as when pouring a liquid from a container, stirring a liquid, or when wind blows across a surface. It is also important in industrial applications, such as in the flow of fluids through pipes or in the operation of turbines.

5. How is shear stress different from other types of stress?

Unlike other types of stress, such as tension or compression, shear stress occurs when forces are applied in a parallel direction. It is also unique in that it does not cause a change in the overall volume of a fluid, but instead causes the fluid to deform and flow.

Similar threads

I So what are the definitions of gas, liquid, solid?
    • Classical Physics
Replies
20
Views
1K
I Work - Energy Principle Application to Fluid Flow
    • Classical Physics
2
Replies
48
Views
2K
A Why are the Navier-Stokes equations inconsistent in this case?
    • Classical Physics
Replies
18
Views
1K
B Question about stress - strain graph and definition of hardness
    • Classical Physics
Replies
4
Views
1K
I What is the meaning of the free surface in fluid mechanics?
    • Classical Physics
Replies
11
Views
992
How to determine shape of surface of a fluid?
    • Classical Physics
Replies
9
Views
1K
Understanding Shearing Stress & Tangential Forces on Fluids
    • Introductory Physics Homework Help
Replies
3
Views
929
Spring and its shear, torsion, tensile stresses...
    • Mechanical Engineering
Replies
1
Views
821
Some questions about Friction in fluid flow
    • Materials and Chemical Engineering
Replies
16
Views
2K
Classical I need some self-contained introductory books on Fluid Mechanics
    • Science and Math Textbooks
Replies
19
Views
3K

Hot Threads

Recent Insights

Back
Top