Difference Between Friction And Viscosity:Comparative Analysis


The behavior of the matter within itself can be understood by the concept of friction and viscosity These are resistive forces that are applicable for different states of matter.

Friction and viscosity are the opposing force that restricts the motion of the matter. These resistive forces have distinct by their properties and causes. This article is concentrated on the study of the difference between friction and viscosity.

Friction

Everybody has experienced the friction force, most probably while walking on grass; this force is exerted between the foot and the grass.

The friction force is defined as “The general resistive force exerted between the two rough surfaces, which opposes the relative motion.”

Difference Between Friction And Viscosity
Friction and Viscosity
Image credits: Image by KLAU2018 from Pixabay 

When a ball is allowed to move on the surface, it moves a certain distance and then stops by itself without any external application of force. This is due to the friction force created between the lower layer of the ball and the upper layer of the surface. When one body tries to move further with the help of another body, this force is produced. It is because no surface is perfectly smooth and uniform. 

Viscosity

Viscosity is the vast concept of fluid dynamics. This is the internal force acting on the fluids.

Viscosity is defined as “the force exerted between the two layers of the fluid which opposes the flow of the fluid.”

Image credits: Image by Steve Buissinne from Pixabay 

When the honey is spilled out of the jar, it flows through some distance. Here there is internal friction that acts between the two layers of the honey. This resists the honey to move further.

Similarly, suppose a ball falls into the water; the different layers of the water restrict the motion of the ball in the water.

The above two examples are due to the internal resistive force of the liquid called viscosity.

Difference Between Friction And Viscosity

Both are the contact force of opposition applied on the matter. They exhibit distinct behavior, some of such behavior are listed in the below table.

FrictionViscosity
It is a force that acts between the two surfaces.It is an internal force acts between the two layers.
Relative velocity gradient does not affect the friction.Viscosity is affected by the relative velocity gradient between the layers.
It is an independent force that resists the motion of the matter; it may be solid or liquid.It is just a measure of force that resists only the liquids.
Friction does not depend on the area occupied between two bodies which are in contact.The area that contacts the two layers of the fluid matters in viscosity.
It is a temperature-independent quantity.It depends on the temperature of the fluid.
The difference in the speed of the two surfaces does not require.The speed difference between the adjacent layers of the fluid shows some impact on the viscosity.
Since this force is applicable for solid and liquid states, the dynamic and static conditions can be applied.The molecules of the liquids are loosely bonded and are mobile molecules; hence there will be no static condition.
All state of matter have experiences the friction.Viscosity is applicable for liquid, and sometimes it holds good for the gaseous state also.

Similarities between the friction and the viscosity

  • Friction and viscosity acts tangentially opposite to the relative motion. Friction retards the motion when two surface are in contact. And viscosity is the intrinsic force that retards the fluid flow between the two layers of the same liquid.
  • The intermolecular force retards the motion which causes both Friction and Viscosity .
  • For both friction and viscosity, the nature of the surface matters.
  • Both friction and viscosity exhibit the intensive property of the matter, as they remain the same even if the amount of the matter changes.
  • More the viscous force acting between the two layers, the fluid flows slowly. Similarly, more the friction force, the motion of the body slows downs.
  • The pressure caused a major impact on both friction and viscosity. The effect of pressure on friction and viscosity is expressed by the graphical representation.
Variation of Friction and Viscosity with Pressure
  • There are mainly two types of friction

Fluid friction acts on the fluid, it means that fluid friction is just another name of Viscosity. This means that viscosity is the derived quantity of the friction force.

Frequently Asked Questions

What are the difference between solid friction and viscosity?

The difference between solid friction and viscosity is listed below.

Solid FrictionViscosity
It is an opposition force that is applied between the two solid surfaces.Viscosity is a type of friction force exerted between the two layers of fluid or liquid.
This is exerted on the solid surface due to the adhesive force acting on the body.This is exerted on the fluid due to the cohesive force acting between the layers of the fluid.
The area enclosed between the two surfaces does not cause any impact on the solid friction.The area enclosed between the two layers of the fluid and the viscosity is directly proportional to each other.
The relative velocity between the two contact surfaces does not matters in solid friction.It is dependent on the relative velocity between the two adjacent layers.
The normal reaction between the solid surfaces does not matter.The normal reaction between the two adjacent layers of the liquid is proportional to the Viscosity.

How does temperature affect the viscosity of the fluid?

The increase in temperature, decreases the viscosity of the fluid.

The cohesive force, which is responsible for the viscosity reduced as the temperature increased. This results in the increase of interchange in the molecules of the fluid. So that fluid starts to flow a little faster.

How is the friction affected by the pressure?

For normal contact pressure between the two surfaces, the friction does not respond proportionally.

If the contact pressure increases, the friction increases rapidly. This is because there will be a change in the linkage between the atoms of the surface in contact. The density of the surface rises and opposes moving away from the contact surface.

Explain the effect of thickness of the fluid on viscosity. 

The effect of thickness over the viscosity can be explained by considering the flow of water, oil and honey.

The thickness of water is less compared to oil, and honey is thicker than oil. Water flows more rapidly than oil, and honey flows slowly compared to oil and water. This means water offers less resistivity to flow and honey offers high resistivity, and oil offers moderate resistivity. It is understood that more the thickness, viscosity increases. 

Does friction cause energy loss?

When the friction is executed between the surfaces, the surface tries to overcome the friction. The energy never lost during this process.

From the law of conservation of energy, the energy change its form in case of friction. Work done by the surface to overcome the friction results in the transformation of kinetic energy into thermal energy. The energy dissipation during the transformation is equal to the heat released.

Keerthi Murthi

I am Keerthi K Murthy, I have completed post graduation in Physics, with the specialization in the field of solid state physics. I have always consider physics as a fundamental subject which is connected to our daily life. Being a science student I enjoy exploring new things in physics. As a writer my goal is to reach the readers with the simplified manner through my articles. Reach me – keerthikmurthy24@gmail.com

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