11.8 Cohesion and Adhesion in Liquids: Surface Tension and Capillary Action

The density is very close to that of pure silver, which is appropriate for this type of ancient coin.

Modern counterfeits are not pure silver.

This brings us back to how the principle came to be.

The king of Syracuse gave Archimedes the task of determining if the royal crown maker was giving a crown of pure gold.
The purity of gold can be determined by color, but other analytical techniques have not yet been developed.
The ancient peoples realized that the density of gold was greater than any other substance.
One day, while at the public baths, he was inspired by the support the water gave his body.

Learn how blocks work.

You can modify the properties of the fluid and blocks with the help of the arrows.

An underwater spider has a bubble in his mouth.

A technician draws blood from a small tube by touching it to a finger.
A premature baby is trying to inflate her lungs.
The attractive forces between atoms and molecules in liquids dominate all of these activities.

Liquids can be held in containers because they are cohesive.

Liquid drops cling to window panes when they are caused by such forces.
In this section, we look at the effects of cohesive and adhesive forces on liquids.

The attractive forces between the same type of molecule are called cohesive forces.

There are attractive forces between different types of molecule.

The soap bubbles in this picture are caused by the same forces.

The surface of a liquid contracts to the smallest possible surface area.
Molecules on the surface are pulled inward by forces.

Molecules inside the liquid have neighbors on all sides.

The surface of a liquid contracts to the smallest possible surface area.

The surface tension is a general effect.

The surface tension is caused by forces between atoms and Molecules.

The attractive forces pull the molecule closer together.
This is an example of a submicroscopic explanation.

Surface tension effects can be explained by a model of a liquid surface acting like a stretched elastic sheet.

The density of the iron needle is greater than that of water.
The stretched surface tries to make the surface smaller or flatter.
The weight of the needle on a small area would break the surface and cause it to sink.

The weight of an insect and an iron needle rest on the surface without being penetrated.

They are supported by the surface of the liquid.

The strength of the cohesive force affects surface tension.

The liquid film tries to reduce the surface area of the wire.

The surface tension of the liquid can be measured accurately.

Liquids form bubbles and droplets because of surface tension.

The inward surface tension force causes bubbles to be spherical and raises the pressure of the gas trapped inside.

There is a bubble.

When the bubble is the smallest, the pressure inside is greatest.
The larger balloon fills the smaller balloon when air is allowed to flow between them.

A sliding wire device is used to measure surface tension.

Since there are two liquid surfaces attached to the wire, the force needed to hold it in place is high.
The force is almost constant as the film is stretched.

Two balloons of different sizes are attached to each end of a tube when the valve is closed.

The smaller balloon shrinks in size when the air moves to fill the larger balloon.
The flow is caused by the smaller balloon having a greater internal pressure than the larger balloon.

The surface tension can be found in Table 11.3, and so can be found directly from the equation.

If a hole were to be made in the bubble, the air would be forced out, the bubble would decrease in radius, and the gauge pressure would decrease to zero.

Our lungs contain hundreds of millions of mucus-lined sacs called alveoli, which are very similar in size and diameter.

Allowing surface tension to contract these sacs will allow you to exhale without muscle action.
Medical patients who have their breathing aided by a positive pressure respirator are allowed to exhale on their own.
Air will leave the lungs even if there is paralysis.
An occasional deep cleansing breath is needed to fully reinflate the alveoli.

We find it natural for our dogs and cats to take a cleansing breath before sleeping.

The bronchial tubes end in alveoli.

The surface tension of their mucous lining helps in exhalation.

The walls of the alveoli have a liquid on them that acts as a surface-tension reducing substance.

The need for the surfactant is caused by the tendency of small alveoli to collapse and the air to fill into the larger alveoli making them even larger.
The surface tension on the alveoli decreases during exhalation as the molecules slide back together.
The wall tension is changed by the surfactant so that small alveoli don't collapse and large alveoli don't expand too much.
This tension change is not shared by detergents, which lowers surface tension.

The lung surfactant's surface tension decreases as the area decreases.

Small alveoli don't collapse and large alveoli aren't able to over expand.

If water enters the lungs, the surface tension is too high and you can't breathe.

This is a serious problem in saving someone's life.
The lungs of newborn infants who are born without this surfactant are difficult to inflate.
It is a leading cause of death for infants in premature births.
The spraying of a surfactant into the infant's breathing passages has achieved some success.
The problem with alveoli is produced by emphysema.
The sacs combine to form larger sacs as the walls of emphysema get worse.
The ability of emphysema victims to exhale is reduced by the larger sacs that produce smaller pressure.
The pressure and volume of air that can be exhaled is a common test for emphysema.

Even the oil from your fingers can affect the surface properties of the needle, so it needs to be very clean.

The bristles will stick together if you pull the brush out.

The surface tension effect goes away as the bristles dry out.

Look at the shape of the loop.
Put a drop of detergent in the middle of the loop.
Put a drop of detergent in it.
For each experiment, the water needs to be replaced and the bowl washed to free it of detergent.

The forces between water and wax are smaller than those between paint and water.

Competition is important in the behavior of liquids.
The angle between the liquid surface and the surface is an important factor in studying the roles of these two forces.
The larger the cohesive force, the bigger the droplets.
The smaller the relative strength, the easier it is to flatten the drop.

The contact angle is the angle between the liquid surface and the surface.

The contact angle is related to the strengths of the forces.

The ratio of cohesive to adhesive forces is larger when it is larger.

The tendency of a fluid to be raised or suppressed in a narrow tube.

When the tube touches a drop, blood is drawn into it.

capillary action is the tendency of a fluid to be raised or suppressed in a narrow tube.

The contact angle given in the table is a factor that affects the effect.

If the fluid is less than, it will be suppressed.
Mercury has a large surface tension and a large contact angle with glass.
The surface of a column of mercury curves downward when placed in a tube.
The surface tension reduces the surface area.
The curved liquid surface in a capillary tube is flattened by surface tension.

The mercury is suppressed in the tube as surface tension flattens it.

The shape of the mercury surface would not be affected by surface tension.
Surface tension exerts an upward force when it flattens the surface.

The height to which capillary action can raise or suppress a liquid in a tube is limited by its weight.

We might see how it makes sense if we look at the different factors.

The height is proportional to the surface tension.
Since a smaller tube holds less mass, the higher the fluid can be raised.
The height is related to fluid density, since a larger density means a larger mass in the same volume.

The larger the tube, the taller it gets.

The height is not significant for large-radius tubes.

To answer this question, calculate the radius of a capillary tube that would raise 100 m to the top of a giant redwood, assuming that it's density is, its contact angle is zero, and its surface tension is the same as that of water.

Every quantity is known except for, and the height to which a liquid will rise as a result of capillary action is given by.

This result is not reasonable.

Tubes with radii as small as are formed when bark in trees moves through the xylem.
The value is about 180 times larger than the radius needed to raise the water.
It is not possible for capillary action alone to be responsible for getting to the top of trees.

The question has not been completely resolved, but it appears that it is pulled up like a chain.

The entire chain is pulled up a notch as each molecule enters a leaf.