# Viscosity vs. Density: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on February 4, 2024
Viscosity is a fluid's resistance to flow, while density is the mass per unit volume of a substance.

## Key Differences

Viscosity is a measure of a fluid's resistance to deformation or flow under an applied force, crucial in understanding how liquids and gases move. Density, in contrast, is a fundamental property of matter representing mass per unit volume, essential in determining buoyancy and material composition.
In practical applications, viscosity is key in industries like lubrication and food processing, where the flow characteristics of fluids are critical. Density plays a significant role in areas such as material science and engineering, where the weight and compactness of materials are important.
Viscosity varies with temperature and composition; for instance, honey has a higher viscosity than water. Density also changes with temperature and pressure but is a more intrinsic property of a substance, like water being denser than oil.
Understanding viscosity helps in predicting how fluids will behave in different environments, crucial for designing pipelines and pumps. Understanding density is vital for applications like ship design, where buoyancy and stability depend on the density of both the ship and the water.
Viscosity and density are both essential physical properties but serve different purposes: viscosity describes a fluid's flow characteristics, while density relates to how compact a substance is.

## Comparison Chart

### Definition

Resistance to flow of a fluid
Mass per unit volume of a substance

### Dependence on Temperature

Viscosity decreases with increasing temperature
Density typically decreases with rising temperature

### Measurement Units

Pascal-seconds (Pa.s) or poise
Kilograms per cubic meter (kg/m³)

### Relevance in Industries

Crucial in fluid dynamics, lubrication
Important in material science, construction

### Variation with Composition

Changes with fluid composition
Relatively intrinsic to material composition

## Viscosity and Density Definitions

#### Viscosity

Viscosity is the property defining the flow resistance of a fluid.
The high viscosity of lava affects its flow during an eruption.

#### Density

Density refers to how compact or concentrated a substance is.
The density of water increases as it is cooled down to 4°C.

#### Viscosity

Viscosity describes how thick or thin a fluid is.
Motor oil's viscosity decreases as it heats up.

#### Density

Density is the mass of a substance per unit of volume.
Lead has a higher density than aluminum.

#### Viscosity

Viscosity is the measure of a fluid's internal resistance to flow.
Honey's high viscosity means it flows more slowly than water.

#### Density

Density is a measure of how much matter is packed into a given space.
Styrofoam's low density makes it lightweight.

#### Viscosity

Viscosity is a fluid's stickiness or semi-fluid consistency.
The viscosity of syrup makes it pour slowly from the bottle.

#### Density

Density determines the heaviness or lightness of a material relative to its size.
Despite its size, the density of aerogel is extremely low.

#### Viscosity

Viscosity indicates a fluid's ability to resist gradual deformation by shear or tensile stress.
Paint's viscosity is adjusted to ensure smooth application.

#### Density

Density is the ratio of mass to volume in a substance.
The high density of gold is evident when lifting a small gold bar.

#### Viscosity

The condition or property of being viscous.

#### Density

The quality or condition of being dense.

#### Viscosity

(Physics) Coefficient of viscosity.

#### Density

The quantity of something per unit measure, especially per unit length, area, or volume.

#### Viscosity

(uncountable) The state of being viscous.

#### Viscosity

A quantity expressing the magnitude of internal friction in a fluid, as measured by the force per unit area resisting uniform flow.

#### Viscosity

A tendency to prolong interpersonal encounters.

#### Viscosity

The quality or state of being viscous.

#### Viscosity

A property possessed by a viscous fluid, being a resistance to the forces causing a fluid to flow, caused by interactions between the molecules of the fluid and between the fluid and the walls of the conduit through which it moves; also, a measure of such a property.

#### Viscosity

Resistance of a liquid to sheer forces (and hence to flow)

## FAQs

#### How is density defined?

As the mass per unit volume of a substance.

#### Does density affect buoyancy?

Yes, it's key in determining an object's buoyancy.

#### How does temperature affect viscosity?

Viscosity generally decreases with increasing temperature.

#### Why is viscosity important in manufacturing?

It determines how fluids flow in processes.

#### Is density constant for a material?

Generally, but it can change with temperature and pressure.

#### How does density relate to material strength?

Higher density often indicates greater material strength.

#### What does viscosity measure in a fluid?

It measures a fluid's resistance to flow.

#### Can viscosity be changed?

Yes, by altering temperature or fluid composition.

#### Do all liquids have the same viscosity?

No, viscosity varies widely among liquids.

#### What factors affect a fluid's viscosity?

Temperature, pressure, and composition.

#### Is density relevant in aerospace engineering?

Absolutely, for material selection and weight calculations.

#### How do lubricants use viscosity?

Their viscosity is tailored for optimal protection and flow.

#### Are viscosity and thickness the same?

Thickness is a layman's term often equated with high viscosity.

#### What is the significance of density in environmental science?

It helps in studying pollution dispersion and material sedimentation.

#### What units are used to measure density?

Kilograms per cubic meter (kg/m³).

#### What role does density play in architecture?

It helps in choosing appropriate materials based on weight and strength.

#### Does viscosity impact fluid dynamics?

Yes, it's crucial in understanding fluid flow behavior.

#### How is density measured?

By dividing mass by volume.

#### Why is density important in shipping?

It affects the weight and stability of cargo.

#### Can gases have viscosity?

Yes, gases also exhibit viscosity.