We Use Water's Unusual Properties To Our Advantage

Dry air is heavier (more dense) than wet air, because water vapor is lighter (less dense) than air. We creatively utilize our knowledge of air density, that is also a function of temperature and pressure, to our advantage.


Baseballs Travel Further in Denver

 

The lower the air pressure, the less dense the air and the less the number of molecules in a unit of air. Thus,  a baseball (or any moving object) experiences less resistance (or drag) to its motion and ends up travelling a longer distance in air of less density.

Source - USAtoday.com

The baseball goes further as the reduced molecules in the air reduce the rate at which its speed slows.
This same effect is seen, but somewhat less obviously when the amount of water vapor increases in the air. Baseballs travel further in moist air where increase in the amount of water vapor reduces the number of molecules subjecting the baseball to resistance.


Indy 500 cars are designed with weather in mind

Source - farcaronline.blogspot.com

Dry dense air also slows a race car. But as high speed is a mandatory requirement, race cars are designed to take advantage of the drag produced by different weather conditions.
Simply speaking, the Indy 500 cars are designed to accept the drag to better hug the track i.e. make the drag push the car onto the track. 
While driving skills are of paramount importance, it is these design modifications that allow a race car to take a turn at 115 mph (without sliding off the track) instead of a slow 70 mph to win the Indianapolis 500.
The driver and pit crew cannot, of course, change the amount of water vapor in the air (humidity) or adjust the atmospheric pressure over the race track. 
All they know is the air temperature and how it is forecast to change while the race is being run. The design allows them to make adjustments to their car that will allow the driver to race with the optimum drag and, hopefully, win the race. 


NASCAR reduces drag with Nitrogen

Source - Nascar.com

Nascar races are run with stock cars - cars we all drive on city streets but strengthened a bit to accommodate more lethal accidents than those we expect during our drives. 
Nascar's solution to reduce air resistance, because they cannot make body design changes, is to use Nitrogen instead of air to inflate the tires of their cars. 
Nitrogen eliminates the small amount of water vapor that exists inside a tire filled with air. As the tire heats up, the water vapor increases the internal pressure in a tire and introduces instabilities that have greater impacts at higher speeds, reduces gas mileage, increases tire wear and reduces tire life. Nitrogen does not display any such negative characteristics.


NASCAR's solution is so appealing that many of us city drivers are starting to fill the tires of our cars with Nitrogen.

Trees are Tall Because Water Can Move Against Gravity

Source - USDA Forest Service

The Sequoia Sempervirens (commonly known as The California Redwood) tree species has the tallest tree in the world, reaching a height of 379.1 feet. This height, a bit short of the estimated 430 feet maximum possible height for a tree, is the result of the tree's ability to develop an internal structure that water can use to rise from tree roots to the topmost leaves of the tree.


Water Molecule

Source- H2O_molecule_scheme_of_dipole.png‎

The unique shape of the water molecule, the shape that makes the water molecule a "polar" molecule, is used by the tree to design its internal water supply system that moves water up the tree. Simply speaking, water moves up the tree because it is "attracted" to the sides of the channels that the tree has created in its internal structure.


Capillary Action

Source - davidnelson.md.

Capillary action is the phenomenon that raises water molecules closest to a vertical surface (of the sides of a tube) because the attraction between the water molecules and the surface material molecules is high and the tube is so small that the water in the tube is unable to form a water surface, as shown on the right. 
When there is a very very tiny or no water surface, then the condition exists (called Capillary action) that all the water  molecules on the surface are "pulled up" and water rises against gravity.
Water in a narrow tube continues to rise due to capillary action, till the forces of attraction (between the water molecules and molecules of the wall material) are able to support the column of water that is formed in the tube. Measurement of this attraction force and calculations of water weight have shown that the maximum height that capillary action can transport water, against the force of gravity, is about 430 feet. So no tree can be taller than 430 feet in height. 


Capillary action is also behind the ability of water to move through soil from high humidity locations to low humidity locations.


Tree Leaves & Branches Are Smallest at the top

Source-hollowcreektreefarm.com

In especially tall trees, the number of branches, the length of a branch, the number of leaves and the size of a leaf all reduce as the height increases. 
These differences with height are due to the amount of water that the tree has available at different heights. As less water is available at greater heights, there is less need for longer branches, lots of leaves and leaves of larger sizes, because transpiration needs are less at greater heights. 
This reducing volume of water with height, produces the typical conical shape of trees.

Water Vapor Permeability

Source -Diffanimals.com

Just like birds of a feather flock together, water is attracted to some surfaces and very little to others. Extracting water, that exists in both vapor and liquid form, from air can, thus, be facilitated either by choosing a naturally-available surface that attracts water droplets and vapor molecules, or by installing a nano substrate, that promotes moisture adsorption and/or absorption, onto the surface. Once water molecules arrive at the surface, one of two situations exist: Either the surface undergoes a transformation (that may be permanent or temporary) or the surface undergoes no transformation. The energy requirements to collect the water from these different surfaces are different. 


Water Vapor Permeability (WVP)

Source - CopyrightFreeImages.com

WVP is the rate of water vapor transmission per unit area per unit of vapor pressure differential.  If a water drop on a leaf stays as a drop the WVP of the leaf is near zero. Such a situation occurs when the attraction between water molecules is very much greater than the attraction between water molecules and the molecules at the surface of the leaf that come into contact with the water molecules. 

Source - psrc.usm.edu

Many novel membranes have been created that are almost impermeable to air but are permeable to water vapor. 


Nafion, a Dupont product, is one such membrane that is commercially available. Such membranes, which do not permit air to pass through them, but permit passage of water vapor, find important applications in power source, pharmaceutical and biotech industries.


The side of the Nafion membrane that comes in contact with water vapor develops a surface concentration in equilibrium with the vapor. With increase in time, the migration of water vapor occurs along the thickness direction of the membrane. 


Initially, a new dry Nafion membrane is impervious to air and large molecules of water and water vapor. However, once the membrane has been exposed to water vapor, the membrane chemically attracts the vapor and absorbs the vapor. The part of the membrane that absorbs water vapor becomes conducting to the vapor, while the rest of the membrane remains dry and non-conducting. Therefore, vapor transport through the
membrane is zero in the initial stages and gains speed once the moisture concentration on the far side of the membrane becomes greater than zero.

Water Helps A Gecko Walk On Ceilings With a Small Human Child On Its Back

In the Simpsons Movie, Homer had to hold up his pig upside down, to realize his dream of owning a pig that could imitate a spider and walk on ceilings. He could have realized this dream and  

Source-thesharkguys.com

Gecko climbing the wall.
(Credit: iStockphoto/Luis Carlos Torres)

watched his pig from his favorite couch, if he had only known about nature's ingenious design of the underside of a Gecko's foot.All he really had to do was modify the underside of his pig's feet (to make them similar to the feet nature gave the common household gecko) and add a little moisture to the air in the room. 

Van Der Walls Forces
At the molecular level, all molecules experience some level of attraction. This 
attraction is electrical in nature and arises from the temporary fluctuating dipoles that are created by electron motion. 
A molecule that typically is symmetrical and has no electrical distortion, can exhibit an electrical charge when either a lot of its electrons happen to be in the same area of the molecule or when influenced by another molecule that is exhibiting an electrical charge. This temporary "sloshing around" of electrons creates fluctuating dipoles even in a 'normally' benign molecule.

Source-Labwater.com

And, as one would expect, in the presence of water that exhibits a permanent dipole charge, the molecular attraction is strong, long-lived and nearly permanent.


The Underside of the Gecko's Foot

Different types of geckos have different 'looking feet' but they all share a common characteristic - they can all interact with all kinds of surfaces at the molecular level and use this molecular attraction to scamper up walls and run around on the ceiling.

Different Gecko Foot Designs
Source-geckolab.lclark.edu 

Gecko Foot Hairs & Strands
Source-Sciencephoto.com

Each toe of a gecko's foot contains hundreds of pad like ridges. On each ridge are millions of hairs that each divide, at their ends, into smaller strands. These strands are so tiny that the molecules at their ends interact with the molecules of the surface the gecko is walking on. The presence of even minuscule amounts of water strengthens these attractive bonds between the gecko's strands and the surface. Maybe, this is why, the Gecko population surges after a monsoon rain when the moisture in the air makes the gecko most mobile on nearly every kind of surface.

In a laboratory environment, the Van Der Walls attraction forces between a single strand and a surface have been measured to support a weight of up to 200 microNewtons - enough to support an ant. With half a million strands on each foot a little gecko walking with 2 million strands can carry a back-pack weighing 90 lbs - the weight of a small child.

Capillary Contribution of water

Liquid bridges formed by water monolayers. between a surface and the strands under a gecko's foot, further increase the attraction bond (due to Van Der Walls forces) that enables the gecko to scamper up walls and walk on ceilings. This increase in adhesion force significantly increases with increase in surface hydrophilicity and increasing levels of humidity.


Capillary forces will be the subject of a future blog.

The task at hand is to use learning from a gecko's foot to use Van Der Walls forces to attract water molecules in the atmosphere using water molecules resident on a hydrophilic surface.