The main difference between viscosity and friction is that Viscosity is a force that measures the internal resistance of a fluid to flow. Friction, on the other hand, is a force that resists motion when two surfaces come in contact.
The other significant difference is that viscosity is also known as internal friction, whereas, friction is known as external friction. Although they both are classified as resistive forces, they are totally opposite to each other. So, without wasting any time, let’s dive right in…!!!
10 Differences Between Viscosity and Friction
| Viscosity | Friction | |
| 1. | Viscosity is a force that measures the internal resistance of a fluid to flow. | Friction is a force that resists motion when two surfaces come in contact. |
| 2. | Factors that affect viscosity are pressure, temperature, and molecular structure of the fluid. | Factors that affect friction are the roughness of the surface in contact and the speed at which they move relative to each other. |
| 3. | Viscosity is used as a property of fluids. | Friction is used as a property of solids and fluids. |
| 4. | Viscosity occurs due to the cohesive forces between the molecules of the fluid. | Friction occurs due to the irregularities on the surfaces of two objects in contact. |
| 5. | It is a scalar quantity | It is a vector quantity. |
| 6. | The symbol for viscosity is (η) eta. | The symbol for friction is (μ) mu. |
| 7. | Viscosity is measured using Viscometer. | Friction is measured using the Friction coefficient. |
| 8. | The SI unit of viscosity is Pa·s (Pascal second) or cP (centipoise). | The SI unit of friction is Newton (N). |
| 9. | It helps to determine the flow behavior of the fluids such as in pipelines or pumps. | It helps to determine the efficiency of machines and the wear and tear on their moving parts. |
| 10. | An example of viscosity is honey flows more slowly than water. | An example of friction is car slows down when the brakes are applied. |
What is Viscosity?
By definition, Viscosity is a force that measures the internal resistance of a fluid to flow. By knowing viscosity, we can easily determine the thickness and thinness of any given fluid.
It is basically used to understand the effects on flow behavior such as whether the flow of the fluid is laminar or turbulent. Temperature, pressure, and shear rate are determining factors in terms of viscosity. In addition, Viscosity can be reduced by adding a thinner or heating the fluid.
Viscosity can be variable for different types of fluids. For example, Newtonian fluids have a constant viscosity regardless of the shear rate. Non-Newtonian fluids, on the other hand, have a variable viscosity depending on the shear rate.
Types of Viscosity
In general, there are two types of viscosity. These are Dynamic Viscosity and Kinematic Viscosity. By definition, Dynamic Viscosity is the measure of internal resistance of the fluid against the flow.
Whereas, kinematic viscosity is the ratio of dynamic viscosity to density. It is also known as Momentum Diffusivity. Mathematically, it is given by:
where,
ν = Kinematic Viscosity
ρ = density of a fluid
μ = Dynamic Viscosity
Properties of Viscosity
Some of the properties of viscosity are:
- Viscosity decreases with an increase in temperature.
- Viscosity increases with an increase in pressure.
- Viscosity affects flow behavior
- Viscosity is a scalar quantity, etc.
Examples of Viscosity
Some of the examples of viscosity are:
- Milk has low viscosity
- Water has low viscosity
- Fruit juice has low viscosity
- Vegetable oil has a high viscosity
- Maple syrup has a high viscosity
- Honey has a high viscosity, etc.
What is Friction?
By definition, friction is a force that resists the motion when two surfaces come in contact. One can say that it simply opposes the motion between two surfaces when they are in contact. The reason behind the frictional forces is the roughness of the surfaces in contact.
By knowing friction, we can easily determine the efficiency of machines and the wear and tear on their moving parts. Friction, also known as external friction causes the generation of heat. This is the sole reason why lubrication or polish is used on surfaces that are in contact during motion.
Types of Friction
In general, there are four types of friction. These are static friction, sliding friction, rolling friction, and fluid friction.
- Static Friction is a type of frictional force that acts between two surfaces when they are at rest (static) with respect to each other.
- Sliding Friction is a type of frictional force that opposes the motion between two surfaces when they are sliding against each other.
- Rolling Friction is a type of frictional force that opposes the motion between two surfaces when they are rolling against each other.
- Fluid Friction is a type of frictional force that opposes the motion between the layers of the fluids when they are flowing relative to each other.
Properties of Friction
Some of the properties of Friction are:
- Friction acts in the opposite direction to the motion.
- Friction depends on the normal force and nature of the surfaces in contact.
- Friction generates heat and can cause wear and tear.
- Friction is a vector quantity, etc.
Examples of Friction
Some examples of friction include:
- When we walk
- When we write
- Application of brake on tire
- When we skate
- Flying of airplane
- Lighting a Matchstick, etc.
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