Liquids Flashcards
cohesion
the attraction force between molecules of the same substance
an intermolecular attraction
the formation of water droplets on the surface tension of a liquid due to cohesion
For Example:
water droplets sticking to each other
adhesion qualities
the attraction force between different molecules
an intramolecular attraction
the spreading of liquid on a solid surface is due to adhesion
For example:
water sticks to other things
Capillary action
caused by the adhesive, cohesive and surface tension forces
allows a thin film of liquid to be drawn up the sides of a glass tube or forced down the tube, depending on the liquid being used
considered when designing and developing many commercial products – lamp oils and lamp wicks
nature displays capillary action when water rises in soil and maple sap flows in a tree and the circulation of blood in your body
What determines the degree of capillary action?
depends on what the material is made of, its shape and cellular structure
for example:
the height water can be raised in a glass tube depends on the diameter of the tube
meniscus
the curve formed by capillary action
molecules that demonstrate greater cohesion than adhesion will..
fall in a capillary tube/graduated cylinder
a smile!
molecules that demonstrate greater adhesion than cohesion will…
rise in a capillary tube/graduated cylinder
a frown!
cohesive forces
forces of attraction between molecules that are alike
gives solids rigidity and strength
cause a greater attractive force between molecules at the surface of the material
adhesive forces
forces of attraction between unlike molecules
glue can supply the adhesive forces used in binding surfaces together
pencil lead, ink, chalk and paint
What is the difference between cohesion and adhesion?
They are nouns that describe the state of molecules sticking together.
Adhesion refers to clinging of unlike molecules and cohesion refers to the clinging of like molecules
Cohesion is the tendency of water molecules to stick to other water molecules while adhesion is the tendency of water to stick to other substances
surface tension
cohesive forces between molecules of the same material cause a greater attractive force between molecules at the surface of the material
causes dewdrops, raindrops, and soap bubbles to form a sphere
detergents break down the surface tension and permit the direct to be washed away
Why does a meniscus form a larger surface area?
molecules on the surface are spread
their cohesive forces create the tension on the surface of the liquid
This tension creates an “elastic skin” known as surface tension!
volatility
the ability of a liquid to be changed to a vapor
vapor
the word used to describe the molecules of a liquid that escape the surface of the liquid and form a gas
Why does gas have octane ratings?
describes the ability of the fuel to vaporize and burn inside an automobile engine
the lower the octane, the more volatile the gasoline
pings and knocks indicate the fuel is not burning correctly
Why must more volatile liquids have greater care?
volatile liquids burst into flames easily
they displace the oxygen in the air we breath
Viscosity
the ease in which a liquid flows
A fluid that has high viscosity does not..
flow easily
there is more friction between the molecules of the fluid which slows its flow
Why is viscosity an important characteristic when developing and using lubricating oils?
The higher viscosity of the lubricating oil helps prevent wear on the internal parts of the engine
How do you measure viscosity of a fluid?
measuring the time required for a given amount of fluid to pass through a long tube of a small diameter
the longer the time, the higher the viscosity rating
viscosity ratings are expressed in weight
an example would be the level of 40 weight oil
an oil with a higher viscosity rating will have a higher weight assigned to it
Specific gravity
the ratio of the weight of a liquid to the weight of an equal volume of water
important when checking:
- antifreeze
- gas
- alcohols
- acids
indication that the correct amount of chemical is in the liquid
hydrometer
easiest way to check the specific gravity of liquids
the greater the specific gravity of the liquid, the higher the float in the hydrometer will rise
specific gravity formula
weight of liquid / weight of equal volume of water
Pascal’s law
pressure is instantly transmitted throughout a liquid
if you change pressure at any point in a fluid container, it equalizes itself across all the fluid
Squeeze one point of water in a balloon and the pressure evens itself out across the whole water balloon
Hydraulic press
takes advantage of Pascal’s law
extreme pressure can be exerted with a small effort
the pressure generated by the small piston exerts a force on the larger piston equal to the ratio of the areas of the pistons
force 2 = area 2 x force 1 / area 1
Hydraulic system equation
force 2 / area 2 = force 1 / area 1
force is in reference to the force being applied and area is referring to the space in which the force is pushing upon
Buoyancy
the force of a liquid which pushes an object up
Archimedes
discovered buoyancy
when a body is placed in a fluid, it is buoyed up by a force equal to the weight of the displaced fluid
in order for an object to float in water, the buoyancy force must be equal to the entire weight of the object
Why do steel ships float?
They enclose a large volume of space
The density of the entire ship is less than the density of the water
