But how do scientists determine the times? No, they do not send meteorologists out on a ladder and have them crane their necks. No observation is involved at all—just math. By crunching the numbers based on the orbit of the Earth around the Sun, the sunrise and sunset times can be calculated long in advance.
Richard Williams, a meteorologist at the National Weather Service, explains that published times are only approximations of what we observe with our naked eyes:
The time of sunrise and sunset varies with day of the year, latitude, and longitude. The published sunrise and sunset times are calculated without regard to surrounding terrain. That is, all computations are made for a sea-level horizon, even in mountainous areas. Thus the actual time of sunrise at a particular location may vary considerably from the “official” time.
When we observe sunset, the Sun has already gone below the horizon. The Earth’s atmosphere “bends” the Sun’s rays and delays the sunset by about three minutes. Likewise with sunrise, the sun makes its first appearance before it would on a planet with no atmosphere. We actually get five to ten minutes of extra sunlight due to this effect.
Submitted by a caller on the Larry Mantle Show,
Pasadena, California.
* * *
WHAT ACCOUNTS FOR THE VARYING AMOUNTS
OF STATIC ELECTRICITY FROM DAY TO DAY?
WHY IS THERE MORE STATIC ELECTRICITY IN
THE WINTER THAN DURING THE SUMMER?
* * *
With the help of Richard A. Anthes, president of the University Corporation for Atmospheric Research, we can lay out the answer to this Imponderable with a logical precision that Mr. Wizard would admire.
1. Static electricity relies upon the buildup of an electrical charge difference between two objects and the sudden release of this difference in an electrical spark.
2. In order to build up a charge difference sufficient to create static electricity, there should not be much electrical conductivity in the air.
3. The conductivity of moist air is greater than the conductivity of dry air.
4. Relative humidity inside houses or other buildings is usually much lower in the winter than the summer.
5. Therefore, static electricity is more likely to occur in the winter than in the summer.
Static electricity can occur in the summer if the humidity happens to be low that day or if air conditioning dehumidifies the air inside.
Submitted by Reverend Ken Vogler of Jeffersonville, Indiana.
* * *
WHY DON’T TREES ON A SLOPE GROW
PERPENDICULAR TO THE GROUND AS
THEY DO ON A LEVEL SURFACE?
* * *
Trees don’t give a darn if they’re planted on a steep hill in San Francisco or a level field in Kansas. Either way, they’ll still try to reach up toward the sky and seek as much light as possible.
Botanist Bruce Kershner told Imponderables that
this strong growth preference is based on the most important of motivations: survival. Scientifically, this is called “phototropism,” or the growth of living cells toward the greatest source of light. Light provides trees with the energy and food that enable them to grow in the first place.
There is also another tropism (involuntary movement toward or away from a stimulus) at work—geotropism—the movement away from the pull of gravity (roots, unlike the rest of the tree, grow toward the gravitational pull). Even on a hill slope, the pull of gravity is directly down, and the greatest source of average light is directly up. In a forest, the source of light is only up.
There are cases where a tree might not grow directly up. First, there are some trees whose trunks grow outward naturally, but whose tops still tend to point upward. Second, trees growing against an overhanging cliff will grow outward on an angle toward the greatest concentration of light (much like a house plant grows toward the window). Third, it is reported that in a few places on earth with natural geomagnetic distortions (e.g., Oregon Vortex, Gold Hill, Oregon), the trees grow in a contorted fashion. The gravitational force is abnormal but the light source is the same.
John A. Pitcher, of the Hardwood Research Council, adds that trees have developed adaptive mechanisms to react to the sometimes conflicting demands of phototropism and geotropism:
Trees compensate for the pull of gravity and the slope of the ground by forming a special kind of reaction wood. On a slope, conifer trees grow faster on the downhill side, producing compression wood, so named because the wood is pushing the trunk bole uphill to keep it straight. Hardwoods grow faster on the uphill side, forming tension wood that pulls the trunk uphill to keep it straight.
Why softwoods develop compression wood and hardwoods develop tension wood is one of the unsolved mysteries of the plant world.
We’ll put that unsolved mystery on our to-do list.
Submitted by Marvin Shapiro of Teaneck, New Jersey.
Thanks also to Herbert Kraut of Forest Hills, New York;
and Gregory Laugle of Huber Heights, Ohio.
* * *
WHY ARE LAKES WINDIER AT MIDDAY
THAN DURING MORNING OR NIGHT?
* * *
Richard Williams, a meteorologist at the National Weather Service’s National Severe Storms Forecast Center, has actually paid cash money to buy Imponderables books (we knew there was something we like about him), and sent in his own Imponderables in the past. And now he was kind enough to send us a detailed letter on the subject at hand.
Williams emphasizes that it is windier over land as well as lake during midday. However, the wind increase is accentuated over the relatively smooth, open surface of a lake.
Often, the lowest layers of the atmosphere are at rest during the night and more active or turbulent by day. At night, particularly on clear nights, the earth’s surface cools along with the adjacent lowest layers of the atmosphere. The lower layers cool faster than the higher layers, producing a “stable” temperature regime with cool air at ground level and relatively warmer air above the surface.
Under these conditions a temperature inversion will form a few hundred feet above the earth’s surface. An inversion is a vertical zone in which temperatures rise with increasing altitude versus the normal cooling. The inversion serves as a barrier or boundary—separating the near-surface air from wind flow aloft. Often at night, calm or very light wind flow will occur at ground level even though the winds aloft continue with little change in speed from day to night.
After sunrise, if the day is sunny or at least partially so, the sun warms the ground. In the lowest layers of the atmosphere, warm, turbulent mixing occurs and the inversion boundary disappears. Once this happens, the general wind flow resumes at the surface. Winds that were probably present during the night just a few hundred feet above the surface can again be felt at ground level. The midday increase in winds is most pronounced over water where there is less resistance to wind flow.
Another effect occurs along a coastline and over large lakes. Above a large body of water, local land-to-water wind circulations develop due to the unequal heating of water and land surfaces. This differential heating during the afternoon produces a water-to-land breeze, known as the sea breeze or lake breeze. At night a weaker land-to-water low level breeze can occur: the land breeze.
Submitted by C. Loewenson of New York, New York.
* * *
WHERE DOES THE MOISTURE GO WHEN WISPS OF
CLOUDS DISAPPEAR IN FRONT OF YOUR EYES?
* * *
A few facts about clouds will give us the tools to answer this question:
1. A warm volume of air at saturation (i.e., 100 percent relative humidity), given the same barometric pressure, will hold more water vapor than a cold volume of air. For example, at 86° Fahrenheit, seven times as much water vapor can be retained as at 32° Fahrenheit.
2. Therefore, when a volume of air cools, its relative humidity increases until it reaches 100 percent relative humidity. This point is called the dew point temperature.
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3. When air at dew point temperature is cooled even further, a visible cloud results (and ultimately, precipitation).
4. Therefore, the disappearance of a cloud is caused by the opposite of #3. Raymond E. Falconer, of the Atmospheric Sciences Research Center, explains:
As a volume of air moves downward from lower to higher barometric pressure, it becomes warmer and drier, with lower relative humidity. This causes the cloud to evaporate.
When we see clouds, the air has been rising and cooling with condensation of the invisible water vapor into visible cloud as the air reaches the temperature of the dew point. When a cloud encounters drier air, the cloud droplets evaporate into the drier air, which can hold more water vapor.
When air is forced up over a mountain, it is cooled, and in the process a cloud may form over the higher elevations. However, as the air descends on the lee side of the mountain, the air warms up and dries out, causing the cloud to dissipate. Such a cloud formation is called an orographic cloud.
Submitted by Rev. David Scott of Rochester, New York.
* * *
WHY IS THE BARK OF A TREE DARKER
THAN THE WOOD INSIDE?
* * *
Depends on how and where you slice it. Actually, there is more than one bark in a tree. A living inner bark, called the phloem, is relatively light in color and is composed of the same cells as wood. When the enzymes in phloem are exposed to air, oxidation darkens it, just as a peeled apple or banana discolors when exposed to air.
The outer bark of a tree, called the rhytidome, is dark. Dark and dead. The main purpose of the rhytidome is to protect the inside of the tree, so it contains tannins (acids used in tanning and in medicine), phenols, and waxes, which help form a barrier to protect the tree from invading fungi and insects. These protective substances are the source of the outer bark’s dark color. The degree to which the color of outer and inner barks of trees compare to their wood varies considerably, as John A. Pitcher, of the Hardwood Research Council, explains:
The concentration of tannins, waxes, and phenols varies from tree to tree and between species. Tannins are still extracted from bark for use in the leather curing process (e.g., genuine oak-tanned leathers). On the other hand, [lighter-colored] wine bottle corks come from the dead inner bark of the corkbark oak, Quercus suber. The bark is nearly the same color as the wood itself.
Submitted by Jill Davies of Forest, Mississippi.
* * *
IF NOTHING STICKS TO TEFLON, HOW DO
THEY GET TEFLON TO STICK TO THE PAN?
* * *
They,” of course, is Du Pont, which owns the registered trademark for Teflon and its younger and now more popular cousin, Silverstone. G. A. Quinn, of Du Pont, told Imponderables that the application of both is similar:
When applying Silverstone to a metal frypan, the interior of the pan is first grit-blasted, then a primer coat is sprayed on and baked. A second layer of Polytetrafluoroethylene (PTFE) is applied, baked and dried again. A third coat of PFTE is applied, baked and dried.
About the only thing that sticks to PTFE is PTFE. So, the 3-coat process used in Silverstone forms an inseparable bond between the PTFE layers and the primer coat bonds to the rough, grit-blasted metal surface.
Du Pont has recently introduced Silverstone Supra, also a three-layer coating that is twice as durable as conventional Silverstone.
Submitted by Anthony Virga, of Yonkers, New York.
* * *
WHY DOESN’T GLUE GET
STUCK IN THE BOTTLE?
* * *
There are two basic reasons:
1. In order for glue to set and solidify, it must dry out. Latex and water-based glues harden by losing water, either by absorption into a porous substrate (the surface to be bonded) or by evaporation into the air. The glue bottle, at least if it is capped tightly, seals in moisture.
2. Different glues are formulated to adhere to particular substrates. If the glue does not have a chemical adhesion to the substrate, it will not stick. For example, John Anderson, technical manager for Elmer’s Laboratory (makers of Elmer’s Glue-All), told us that the Elmer’s bottle, made of polyethylene, does not provide a good chemical adhesion for the glue.
Even when the cap is left off, and the glue does lose water, the adhesion is still spotty. We can see this effect with the cap of many glue bottles. In most cases, dried glue can and does cake onto the tip after repeated uses. But Anderson points out that the adhesion is “tenuous,” and one can easily clean the top while still wet and remove the glue completely. Likewise, if you poured Elmer’s on a drinking glass, it might adhere a little, but you could easily wipe it off with a cloth or paper towel, because the glue cannot easily penetrate the “gluee.”
Submitted by Jeff Openden of Northridge, California.
* * *
WILL SUPER GLUE STICK TO TEFLON?
* * *
We were wary of contacting Loctite and Teflon about this almost metaphysical Imponderable, for it would be like prying a confession from the immovable object (Teflon) and the unstoppable force (Super Glue) that one of their reputations was seriously exaggerated. But we are worldly wise in such matters. After all, we had already cracked the centuries-old conundrum about “If nothing sticks to Teflon, how do they get Teflon to stick to the pan?” in Why Do Clocks Run Clockwise? We were ready for a new challenge.
So first we contacted Du Pont, the chemical giant that markets Teflon, a registered trademark for polytetrafluoroethylene (which, for obvious reasons, we’ll call ptfe). As we expected, Kenneth Leavell, research supervisor for Du Pont’s Teflon/Silverstone division, took a hard line. He firmly holds the conviction that Super Glue won’t stick to Teflon, at least “not very well and certainly not reliably.” Here are some of the reasons why not:
1. The combination of fluorine and carbon in ptfe forms one of the strongest bonds in the chemical world and one of the most stable.
2. The fluorine atoms around the carbon-fluorine bond are inert, so they form an “impenetrable shield” around the chain of carbon atoms, keeping other chemicals from entering. As Leavell puts it,
Adhesives need to chemically or physically bond to the substrate to which they are applied. Ptfe contains no chemical sites for other substances to bond with.
3. As we just learned with glue bottles, adhesives need to wet the substrate directly or creep into porous areas in the substrate. But the low surface energy of ptfe prevents wetting and bonding. Leavell compares it to trying to get oil and water to stick together.
And then he lays down the gauntlet:
Super Glue is “super” because of its speed of cure and relatively strong bonds. As an adhesive for ptfe, it’s no better than epoxies, polyurethanes, etc., would be.
So, the immovable object claims near invincibility. How would the unstoppable force react? We contacted Loctite’s Richard Palin, technical service adviser. And he folded like a newly cleaned shirt. Yes, Palin admitted, Teflon lacks the cracks necessary for Super Glue to enter in order to bond properly; there would be nowhere for the glue to get into the pan. Yes, he confessed, the critical surface tension is too low for the adhesive to wet the surface. Yes, he broke down in sobs, Super Glue would probably just bead up if applied to a Teflon pan.
Just kidding, actually. Palin -didn’t seem upset at all about Super Glue’s inability to stick to Teflon. By all accounts, there doesn’t seem to be much demand for the task.
Submitted by Bill O’Donnell of Eminence, Missouri.
* * *
WHY DOESN’T A CLINICAL THERMOMETER
REGISTER ROOM TEMPERATURE WHEN YOU
TAKE IT OUT OF YOUR MEDICINE CABINET?
* * *
We trust thermometers. If our temperature is 98.8°, we say we have a fever. But when we take out the thermometer, the temperature reading seems to have no correlation to reality. Why isn’t the thermometer sensitive enough to know that room temperature is much lower than 96°, or whatever the lowest number on the thermom
eter is?
In order to understand this phenomenon, we need a crash course in thermometer anatomy. The metal part of the thermometer that we stick into our mouths is the bulb. The rest of the thermometer is known as the stem. The mercury flows within a capillary, a narrow piece of glass called the mercury column. This column is quite narrow; the mercury in the thermometer is about the width of a human hair. At the base of the mercury column, near the bulb (and the lowest temperature numerals), you’ll see a bump, which is called the constriction.
The constriction is the key to how a clinical thermometer works. To create the constriction, one spot of glass is heated to create a bump—controlled warping. The constriction works as a physical impediment to keep mercury from going down toward the bulb unless you shake it. If you don’t shake the thermometer, the mercury will only go up, not down. The only reason any temperature in a thermometer rises is that the mercury in the bore of the thermometer expands. When the mercury retracts, the constriction is large enough to stop the flow of mercury.
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