Viscosity Chapter 7

Particles in Solids, Liquids, and Gases.

Solid / Liquid / Gas
Shape and volume / Definite shape and volume / No definite shape but a definite volume / No definite shape or volume
Space between particles / Very little space between particles / Moderate space between particles / Large space between particles
Movement / Very little movement of particles / Moderate movement of particles / More freedom of movement
Attraction Forces / Strong attraction forces between particles / Moderate attraction forces / Weak attraction forces

Fluids are liquids and gases because they have more movement and the particles are not held so tightly by attraction forces so that the particles can slip past one another and flow.

A fluid is anything that flows.

Changes of State

Melting ( solid to a liquid) - add heat energy

Freezing (liquid to a solid) – take away energy

Condensation (gas to a liquid)– take away energy

Evaporation (liquid to a gas)- add heat energy

Sublimation (solid to a gas)- add heat energy

Deposition (gas to a solid)– take away energy

Melting

Solid ------Add energy (heat)------Liquid

Little spaces moderate spaces

Little movement moderate movement

Strong attractionmoderate attraction

Adding energy causes the particles to speed up, they collide more often and harder causing them to spread out, which in turn decreases the attraction forces. This is how the solid takes on the properties of a liquid.

Freezing

Liquid------ take away energy (cool it down)------Solid

moderate spacesLittle spaces

moderate movementLittle movement

moderate attractionStrong attraction

Taking away energy causes the particles to slow down, they collide less often , they come closer together, because they are closer together their attraction forces are greater. A liquid will then take on the properties of a solid.

All the changes of states can be explained in this way. You could be asked to explain either one.

Viscosity

-describes the thickness or thinness of a fluid.

- is a fluids resistance to flow

- high resistance means it is thick, it has a high resistance to flow high viscosity = thick

- low resistance means it is thin, it has a low resistance to flow low viscosity = thin

Importance of Viscosity

-Affects the food we eat, your mouth is highly sensitive to viscosity.

-Affects the products we buy You do not want paint that is too thin or thick etc

Viscosity and Flow Rate

Flow rate is how fast or slow a fluid flows or travels from point A to point B.

If a fluid is thick HIGH VISCOSITY = LOW FLOW RATE

If a fluid is thin LOW VISCOSITY = HIGH FLOW RATE

Example: molasses which is thick (high viscosity) will travel slowly (low flow rate)

Water which is thin (low viscosity) will travel fast (high flow rate)

Flow rate = Distance travelled=cm/s

Time taken to travel

Factors Affecting Viscosity

Temperature (Liquids) / Temperature increases, viscosity decreases
-particles have more energy and this decreases the attraction forces allowing them to slip past one another more easily (ex: heat up honey and it moves faster)
Temperature decreases, viscosity increases
Temperature (gases) / Temperature increases, viscosity increases
Gases do not depend on a energy to move further apart- adding energy only increases the number of collisions between particles and therefore increases internal friction.
Temperature decreases, viscosity decreases
Cooler air is thinner.
Concentration / Concentration increases, viscosity increases
The greater the number of particles per volume the greater the internal friction and viscosity.
Add flour to gravy to make it thicker.
Concentration decreases, viscosity decreases
Attraction Forces / Attraction forces decrease, viscosity decreases
Easier for particles to slide past one another.
Attraction forces increases, viscosity increases
Size and complexity of the particle / Bigger, more complex, higher the viscosity
The bigger the particle, the more complex it is and therefore the harder it is to slip past one another.
Smaller, less complex, lower the viscosity