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Chapter 7 -- Part 2
The porous bone is filled with gas at a pressure of 1 atm.
The porous bone needs to be able to hold a pressure of 14 atm.
The bone can survive pressures up to 24 atm.
The decrease in density is caused by the gas in the swim bladder.
The volume of the swim bladder needed to reduce the density of the fish is smaller than that of the porous bone because the density of the gas is negligible.
The density of fish can be altered by their bones or swim bladders.
The cuttlefish alters its density by injecting or withdrawing fluid.
Fish with swim bladders change their density by changing the amount of gas in the bladder.
There are attractive forces on each molecule.
A molecule in the interior of the liquid is surrounded by a group of neighboring molecules.
Net intermolecular force on an interior molecule is zero.
Near the surface of the liquid, the situation is different.
A molecule is pulled towards the interior of the surface because there is no molecule above the surface.
This causes the surface of a liquid to contract.
A surface tension that resists an increase in the free surface of the liquid is caused by this contracting tendency.
It can be shown that surface tension is normal to a line of unit length on the surface.
Molecules near the wall are attracted to a liquid in a vessel.
The attractive cohesive force of the liquid pulls the molecule in the opposite direction.
If the cohesive force is greater than the adhesive force, the liquid wets the container wall and the liquid surface near the wall is curved upward.
The contact angle between glass and water is 25.
When liquid does not wet the wall, there is an angle of contact.
The height of the fluid in the tube is depressed.
The tendency of liquid to assume a spherical shape is a consequence of surface tension.
This tendency can be seen in a liquid outside a container.
The sphere can be seen in the shape of raindrops.
This is the expression for the excess pressure inside the air bubble.
The effects of surface tension can be seen in many areas relevant to the life sciences.
The soil is porous with small particles.
The motion of water through the soil is governed by these spaces.
Water enters the soil through the spaces between the small particles.
If the water did not adhere to the particles, it would run quickly through the soil.
The life of the plant would be severely restricted.
A significant portion of the water that enters the soil is retained because of the capillary action.
The roots must apply a negative pressure to the moist soil to withdraw the water.
The required negative pressure may be high.
The material composition of the soil is one of the factors that affect the SMT.
The quality of the soil is determined by the SMT.
The higher the SMT, the harder it is for the roots to get the water they need.
The dependence of the SMT on the grain size can be understood.
The surface tension is lowest when the soil is filled with water.
The lowest required pressure for the plant roots to withdraw water from the soil is found under these conditions.
Saturated soil isn't the best medium for plant growth.
Coarse-grained soil holds water more tightly than fine-grained soil.
The amount of water in the soil decreases.
The SMT is about 0.19 atm in loam with a 20% moisture content.
The SMT goes up to 0.76 atm when the moisture content goes down to 12%.
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